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 $245.95   12.240%   $276.0543   $276.05   $276.05   $276.10  
  Purchase #2 $229.31   6.291%   $243.7359   $243.74   $243.75   $243.70  
  Purchase #3 $140.88   11.591%   $157.2094   $157.21   $157.20   $157.20  
  Purchase #4 $167.80   9.799%   $184.2427   $184.24   $184.25   $184.20  
  Purchase #5 $230.71   10.538%   $255.0222   $255.02   $255.00   $255.00  
  Purchase #6 $192.35   10.403%   $212.3602   $212.36   $212.35   $212.40  
  Purchase #7 $217.98   5.514%   $229.9994   $230.00   $230.00   $230.00  
  7 purchase totals = $1,424.98       $1,558.6241   $1,558.62   $1,558.60   $1,558.60