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 $121.97   9.308%   $133.323   $133.32   $133.30   $133.30  
  Purchase #2 $46.26   13.329%   $52.426   $52.43   $52.45   $52.40  
  Purchase #3 $203.92   4.318%   $212.7253   $212.73   $212.75   $212.70  
  Purchase #4 $92.94   10.591%   $102.7833   $102.78   $102.80   $102.80  
  Purchase #5 $89.63   5.319%   $94.3974   $94.40   $94.40   $94.40  
  Purchase #6 $203.44   6.241%   $216.1367   $216.14   $216.15   $216.10  
  Purchase #7 $31.97   6.387%   $34.0119   $34.01   $34.00   $34.00  
  7 purchase totals = $790.13       $845.8036   $845.81   $845.85   $845.70