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 $183.47   10.109%   $202.017   $202.02   $202.00   $202.00  
  Purchase #2 $36.63   13.828%   $41.6952   $41.70   $41.70   $41.70  
  Purchase #3 $49.44   3.846%   $51.3415   $51.34   $51.35   $51.30  
  Purchase #4 $179.33   5.338%   $188.9026   $188.90   $188.90   $188.90  
  Purchase #5 $28.55   3.362%   $29.5099   $29.51   $29.50   $29.50  
  Purchase #6 $183.53   12.123%   $205.7793   $205.78   $205.80   $205.80  
  Purchase #7 $96.32   9.824%   $105.7825   $105.78   $105.80   $105.80  
  7 purchase totals = $757.27       $825.0280   $825.03   $825.05   $825.00