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 $97.95   10.695%   $108.4258   $108.43   $108.45   $108.40  
  Purchase #2 $230.89   7.584%   $248.4007   $248.40   $248.40   $248.40  
  Purchase #3 $162.84   3.415%   $168.401   $168.40   $168.40   $168.40  
  Purchase #4 $119.32   5.271%   $125.6094   $125.61   $125.60   $125.60  
  Purchase #5 $216.66   12.611%   $243.983   $243.98   $244.00   $244.00  
  Purchase #6 $76.83   10.755%   $85.0931   $85.09   $85.10   $85.10  
  Purchase #7 $129.88   7.533%   $139.6639   $139.66   $139.65   $139.70  
  7 purchase totals = $1,034.37       $1,119.5769   $1,119.57   $1,119.60   $1,119.60