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 $202.75   12.284%   $227.6558   $227.66   $227.65   $227.70  
  Purchase #2 $206.54   3.203%   $213.1555   $213.16   $213.15   $213.20  
  Purchase #3 $58.79   9.447%   $64.3439   $64.34   $64.35   $64.30  
  Purchase #4 $180.94   9.154%   $197.5032   $197.50   $197.50   $197.50  
  Purchase #5 $173.53   11.797%   $194.0013   $194.00   $194.00   $194.00  
  Purchase #6 $181.75   12.729%   $204.885   $204.89   $204.90   $204.90  
  Purchase #7 $157.64   10.772%   $174.621   $174.62   $174.60   $174.60  
  7 purchase totals = $1,161.94       $1,276.1657   $1,276.17   $1,276.15   $1,276.20