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 $241.97   7.683%   $260.5606   $260.56   $260.55   $260.60  
  Purchase #2 $232.80   12.222%   $261.2528   $261.25   $261.25   $261.30  
  Purchase #3 $97.41   5.590%   $102.8552   $102.86   $102.85   $102.90  
  Purchase #4 $219.47   7.183%   $235.2345   $235.23   $235.25   $235.20  
  Purchase #5 $124.29   10.396%   $137.2112   $137.21   $137.20   $137.20  
  Purchase #6 $151.73   12.323%   $170.4277   $170.43   $170.45   $170.40  
  Purchase #7 $63.98   4.387%   $66.7868   $66.79   $66.80   $66.80  
  7 purchase totals = $1,131.65       $1,234.3288   $1,234.33   $1,234.35   $1,234.40