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 $237.92   3.353%   $245.8975   $245.90   $245.90   $245.90  
  Purchase #2 $213.31   8.267%   $230.9443   $230.94   $230.95   $230.90  
  Purchase #3 $99.66   9.493%   $109.1207   $109.12   $109.10   $109.10  
  Purchase #4 $177.71   6.347%   $188.9893   $188.99   $189.00   $189.00  
  Purchase #5 $11.55   9.270%   $12.6207   $12.62   $12.60   $12.60  
  Purchase #6 $126.98   13.394%   $143.9877   $143.99   $144.00   $144.00  
  Purchase #7 $61.79   11.628%   $68.9749   $68.97   $68.95   $69.00  
  7 purchase totals = $928.92       $1,000.5351   $1,000.53   $1,000.50   $1,000.50