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 $73.66   11.696%   $82.2753   $82.28   $82.30   $82.30  
  Purchase #2 $209.43   5.507%   $220.9633   $220.96   $220.95   $221.00  
  Purchase #3 $164.87   6.214%   $175.115   $175.12   $175.10   $175.10  
  Purchase #4 $131.71   8.289%   $142.6274   $142.63   $142.65   $142.60  
  Purchase #5 $68.80   6.148%   $73.0298   $73.03   $73.05   $73.00  
  Purchase #6 $104.58   6.132%   $110.9928   $110.99   $111.00   $111.00  
  Purchase #7 $234.93   7.746%   $253.1277   $253.13   $253.15   $253.10  
  7 purchase totals = $987.98       $1,058.1313   $1,058.14   $1,058.20   $1,058.10