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 $105.52   7.873%   $113.8276   $113.83   $113.85   $113.80  
  Purchase #2 $155.88   6.331%   $165.7488   $165.75   $165.75   $165.70  
  Purchase #3 $112.32   4.141%   $116.9712   $116.97   $116.95   $117.00  
  Purchase #4 $165.79   4.809%   $173.7628   $173.76   $173.75   $173.80  
  Purchase #5 $179.53   11.691%   $200.5189   $200.52   $200.50   $200.50  
  Purchase #6 $165.54   6.798%   $176.7934   $176.79   $176.80   $176.80  
  Purchase #7 $129.43   6.779%   $138.2041   $138.20   $138.20   $138.20  
  7 purchase totals = $1,014.01       $1,085.8268   $1,085.82   $1,085.80   $1,085.80