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 $238.47   9.441%   $260.984   $260.98   $261.00   $261.00  
  Purchase #2 $119.93   9.383%   $131.183   $131.18   $131.20   $131.20  
  Purchase #3 $71.44   6.855%   $76.3372   $76.34   $76.35   $76.30  
  Purchase #4 $236.35   12.229%   $265.2532   $265.25   $265.25   $265.30  
  Purchase #5 $216.69   10.789%   $240.0687   $240.07   $240.05   $240.10  
  Purchase #6 $199.27   6.709%   $212.639   $212.64   $212.65   $212.60  
  Purchase #7 $172.52   9.237%   $188.4557   $188.46   $188.45   $188.50  
  7 purchase totals = $1,254.67       $1,374.9208   $1,374.92   $1,374.95   $1,375.00