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 $216.32   11.650%   $241.5213   $241.52   $241.50   $241.50  
  Purchase #2 $87.71   8.834%   $95.4583   $95.46   $95.45   $95.50  
  Purchase #3 $117.70   12.603%   $132.5337   $132.53   $132.55   $132.50  
  Purchase #4 $131.34   6.419%   $139.7707   $139.77   $139.75   $139.80  
  Purchase #5 $246.48   10.600%   $272.6069   $272.61   $272.60   $272.60  
  Purchase #6 $218.38   9.587%   $239.3161   $239.32   $239.30   $239.30  
  Purchase #7 $8.60   9.154%   $9.3872   $9.39   $9.40   $9.40  
  7 purchase totals = $1,026.53       $1,130.5942   $1,130.60   $1,130.55   $1,130.60