Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $114.75   13.466%   $130.2022   $130.20   $130.20   $130.20  
  Purchase #2 $183.34   7.410%   $196.9255   $196.93   $196.95   $196.90  
  Purchase #3 $148.71   11.158%   $165.3031   $165.30   $165.30   $165.30  
  Purchase #4 $236.40   10.205%   $260.5246   $260.52   $260.50   $260.50  
  Purchase #5 $208.48   9.781%   $228.8714   $228.87   $228.85   $228.90  
  Purchase #6 $247.38   10.321%   $272.9121   $272.91   $272.90   $272.90  
  Purchase #7 $120.27   7.701%   $129.532   $129.53   $129.55   $129.50  
  7 purchase totals = $1,259.33       $1,384.2709   $1,384.26   $1,384.25   $1,384.20