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 $91.62   3.140%   $94.4969   $94.50   $94.50   $94.50  
  Purchase #2 $139.81   11.861%   $156.3929   $156.39   $156.40   $156.40  
  Purchase #3 $61.31   6.394%   $65.2302   $65.23   $65.25   $65.20  
  Purchase #4 $88.30   6.430%   $93.9777   $93.98   $94.00   $94.00  
  Purchase #5 $33.41   8.709%   $36.3197   $36.32   $36.30   $36.30  
  Purchase #6 $135.96   6.720%   $145.0965   $145.10   $145.10   $145.10  
  Purchase #7 $242.82   5.391%   $255.9104   $255.91   $255.90   $255.90  
  7 purchase totals = $793.23       $847.4243   $847.43   $847.45   $847.40