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 $104.43   12.643%   $117.6331   $117.63   $117.65   $117.60  
  Purchase #2 $216.35   13.830%   $246.2712   $246.27   $246.25   $246.30  
  Purchase #3 $156.76   6.752%   $167.3444   $167.34   $167.35   $167.30  
  Purchase #4 $219.77   12.331%   $246.8698   $246.87   $246.85   $246.90  
  Purchase #5 $215.59   13.375%   $244.4252   $244.43   $244.45   $244.40  
  Purchase #6 $148.29   7.363%   $159.2086   $159.21   $159.20   $159.20  
  Purchase #7 $186.96   7.306%   $200.6193   $200.62   $200.60   $200.60  
  7 purchase totals = $1,248.15       $1,382.3716   $1,382.37   $1,382.35   $1,382.30