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 $237.65   11.434%   $264.8229   $264.82   $264.80   $264.80  
  Purchase #2 $82.29   6.115%   $87.322   $87.32   $87.30   $87.30  
  Purchase #3 $19.99   3.152%   $20.6201   $20.62   $20.60   $20.60  
  Purchase #4 $153.43   5.112%   $161.2733   $161.27   $161.25   $161.30  
  Purchase #5 $204.62   9.745%   $224.5602   $224.56   $224.55   $224.60  
  Purchase #6 $54.66   11.733%   $61.0733   $61.07   $61.05   $61.10  
  Purchase #7 $212.47   13.152%   $240.4141   $240.41   $240.40   $240.40  
  7 purchase totals = $965.11       $1,060.0859   $1,060.07   $1,059.95   $1,060.10