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 $131.50   7.556%   $141.4361   $141.44   $141.45   $141.40  
  Purchase #2 $225.38   9.307%   $246.3561   $246.36   $246.35   $246.40  
  Purchase #3 $148.80   5.476%   $156.9483   $156.95   $156.95   $156.90  
  Purchase #4 $180.63   11.635%   $201.6463   $201.65   $201.65   $201.60  
  Purchase #5 $73.33   5.335%   $77.2422   $77.24   $77.25   $77.20  
  Purchase #6 $234.85   12.326%   $263.7976   $263.80   $263.80   $263.80  
  Purchase #7 $144.75   9.704%   $158.7965   $158.80   $158.80   $158.80  
  7 purchase totals = $1,139.24       $1,246.2231   $1,246.24   $1,246.25   $1,246.10