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 $169.27   10.498%   $187.04   $187.04   $187.05   $187.00  
  Purchase #2 $44.86   6.403%   $47.7324   $47.73   $47.75   $47.70  
  Purchase #3 $227.71   5.566%   $240.3843   $240.38   $240.40   $240.40  
  Purchase #4 $124.80   10.589%   $138.0151   $138.02   $138.00   $138.00  
  Purchase #5 $62.90   7.124%   $67.381   $67.38   $67.40   $67.40  
  Purchase #6 $20.26   4.279%   $21.1269   $21.13   $21.15   $21.10  
  Purchase #7 $184.53   11.280%   $205.345   $205.35   $205.35   $205.30  
  7 purchase totals = $834.33       $907.0247   $907.03   $907.10   $906.90