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 $203.82   10.241%   $224.6932   $224.69   $224.70   $224.70  
  Purchase #2 $155.72   4.229%   $162.3054   $162.31   $162.30   $162.30  
  Purchase #3 $158.58   12.550%   $178.4818   $178.48   $178.50   $178.50  
  Purchase #4 $159.82   9.220%   $174.5554   $174.56   $174.55   $174.60  
  Purchase #5 $94.40   10.699%   $104.4999   $104.50   $104.50   $104.50  
  Purchase #6 $195.63   8.594%   $212.4424   $212.44   $212.45   $212.40  
  Purchase #7 $72.63   8.820%   $79.036   $79.04   $79.05   $79.00  
  7 purchase totals = $1,040.60       $1,136.0141   $1,136.02   $1,136.05   $1,136.00