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 $229.73   7.424%   $246.7852   $246.79   $246.80   $246.80  
  Purchase #2 $237.95   11.213%   $264.6313   $264.63   $264.65   $264.60  
  Purchase #3 $204.56   12.416%   $229.9582   $229.96   $229.95   $230.00  
  Purchase #4 $239.35   10.378%   $264.1897   $264.19   $264.20   $264.20  
  Purchase #5 $113.38   8.357%   $122.8552   $122.86   $122.85   $122.90  
  Purchase #6 $109.32   7.820%   $117.8688   $117.87   $117.85   $117.90  
  Purchase #7 $8.33   9.190%   $9.0955   $9.10   $9.10   $9.10  
  7 purchase totals = $1,142.62       $1,255.3839   $1,255.40   $1,255.40   $1,255.50