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 $216.99   9.429%   $237.45   $237.45   $237.45   $237.50  
  Purchase #2 $137.45   13.841%   $156.4745   $156.47   $156.45   $156.50  
  Purchase #3 $241.57   11.855%   $270.2081   $270.21   $270.20   $270.20  
  Purchase #4 $132.92   12.816%   $149.955   $149.96   $149.95   $150.00  
  Purchase #5 $188.70   7.779%   $203.379   $203.38   $203.40   $203.40  
  Purchase #6 $50.82   10.601%   $56.2074   $56.21   $56.20   $56.20  
  Purchase #7 $8.46   8.498%   $9.1789   $9.18   $9.20   $9.20  
  7 purchase totals = $976.91       $1,082.8529   $1,082.86   $1,082.85   $1,083.00