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 $66.68   10.134%   $73.4374   $73.44   $73.45   $73.40  
  Purchase #2 $65.51   5.752%   $69.2781   $69.28   $69.30   $69.30  
  Purchase #3 $97.85   4.663%   $102.4127   $102.41   $102.40   $102.40  
  Purchase #4 $102.26   4.622%   $106.9865   $106.99   $107.00   $107.00  
  Purchase #5 $56.41   11.232%   $62.746   $62.75   $62.75   $62.70  
  Purchase #6 $210.39   9.307%   $229.971   $229.97   $229.95   $230.00  
  Purchase #7 $242.48   8.609%   $263.3551   $263.36   $263.35   $263.40  
  7 purchase totals = $841.58       $908.1868   $908.20   $908.20   $908.20