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 $241.85   11.145%   $268.8042   $268.80   $268.80   $268.80  
  Purchase #2 $37.83   4.248%   $39.437   $39.44   $39.45   $39.40  
  Purchase #3 $222.80   5.614%   $235.308   $235.31   $235.30   $235.30  
  Purchase #4 $68.57   6.378%   $72.9434   $72.94   $72.95   $72.90  
  Purchase #5 $181.96   7.435%   $195.4887   $195.49   $195.50   $195.50  
  Purchase #6 $16.91   5.153%   $17.7814   $17.78   $17.80   $17.80  
  Purchase #7 $187.54   7.287%   $201.206   $201.21   $201.20   $201.20  
  7 purchase totals = $957.46       $1,030.9687   $1,030.97   $1,031.00   $1,030.90