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 $234.50   5.650%   $247.7493   $247.75   $247.75   $247.70  
  Purchase #2 $28.64   11.471%   $31.9253   $31.93   $31.95   $31.90  
  Purchase #3 $173.78   4.816%   $182.1492   $182.15   $182.15   $182.10  
  Purchase #4 $232.51   4.436%   $242.8241   $242.82   $242.80   $242.80  
  Purchase #5 $227.30   5.414%   $239.606   $239.61   $239.60   $239.60  
  Purchase #6 $245.96   4.687%   $257.4881   $257.49   $257.50   $257.50  
  Purchase #7 $162.56   7.498%   $174.7487   $174.75   $174.75   $174.70  
  7 purchase totals = $1,305.25       $1,376.4907   $1,376.50   $1,376.50   $1,376.30