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 $182.60   11.709%   $203.9806   $203.98   $204.00   $204.00  
  Purchase #2 $151.77   7.522%   $163.1861   $163.19   $163.20   $163.20  
  Purchase #3 $205.90   11.231%   $229.0246   $229.02   $229.00   $229.00  
  Purchase #4 $31.65   8.832%   $34.4453   $34.45   $34.45   $34.40  
  Purchase #5 $193.47   5.283%   $203.691   $203.69   $203.70   $203.70  
  Purchase #6 $62.94   6.816%   $67.23   $67.23   $67.25   $67.20  
  Purchase #7 $152.88   3.710%   $158.5518   $158.55   $158.55   $158.60  
  7 purchase totals = $981.21       $1,060.1094   $1,060.11   $1,060.15   $1,060.10