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 $45.44   4.198%   $47.3476   $47.35   $47.35   $47.30  
  Purchase #2 $169.39   13.576%   $192.3864   $192.39   $192.40   $192.40  
  Purchase #3 $55.47   6.334%   $58.9835   $58.98   $59.00   $59.00  
  Purchase #4 $190.54   4.783%   $199.6535   $199.65   $199.65   $199.70  
  Purchase #5 $52.73   4.133%   $54.9093   $54.91   $54.90   $54.90  
  Purchase #6 $155.74   7.349%   $167.1853   $167.19   $167.20   $167.20  
  Purchase #7 $249.56   5.168%   $262.4573   $262.46   $262.45   $262.50  
  7 purchase totals = $918.87       $982.9229   $982.93   $982.95   $983.00