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 $127.76   11.123%   $141.9707   $141.97   $141.95   $142.00  
  Purchase #2 $27.84   11.256%   $30.9737   $30.97   $30.95   $31.00  
  Purchase #3 $222.96   4.316%   $232.583   $232.58   $232.60   $232.60  
  Purchase #4 $238.86   7.721%   $257.3024   $257.30   $257.30   $257.30  
  Purchase #5 $72.82   5.820%   $77.0581   $77.06   $77.05   $77.10  
  Purchase #6 $29.43   8.715%   $31.9948   $31.99   $32.00   $32.00  
  Purchase #7 $206.99   11.292%   $230.3633   $230.36   $230.35   $230.40  
  7 purchase totals = $926.66       $1,002.2460   $1,002.23   $1,002.20   $1,002.40