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 $216.27   12.501%   $243.3059   $243.31   $243.30   $243.30  
  Purchase #2 $24.43   8.480%   $26.5017   $26.50   $26.50   $26.50  
  Purchase #3 $71.50   9.776%   $78.4898   $78.49   $78.50   $78.50  
  Purchase #4 $6.94   10.153%   $7.6446   $7.64   $7.65   $7.60  
  Purchase #5 $115.87   5.107%   $121.7875   $121.79   $121.80   $121.80  
  Purchase #6 $68.56   7.570%   $73.75   $73.75   $73.75   $73.80  
  Purchase #7 $168.35   12.681%   $189.6985   $189.70   $189.70   $189.70  
  7 purchase totals = $671.92       $741.1780   $741.18   $741.20   $741.20