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 $116.86   8.858%   $127.2115   $127.21   $127.20   $127.20  
  Purchase #2 $32.73   4.186%   $34.1001   $34.10   $34.10   $34.10  
  Purchase #3 $77.55   3.280%   $80.0936   $80.09   $80.10   $80.10  
  Purchase #4 $169.47   3.648%   $175.6523   $175.65   $175.65   $175.70  
  Purchase #5 $197.88   12.758%   $223.1255   $223.13   $223.15   $223.10  
  Purchase #6 $222.55   9.668%   $244.0661   $244.07   $244.05   $244.10  
  Purchase #7 $73.55   13.867%   $83.7492   $83.75   $83.75   $83.70  
  7 purchase totals = $890.59       $967.9983   $968.00   $968.00   $968.00