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 $45.62   5.206%   $47.995   $48.00   $48.00   $48.00  
  Purchase #2 $195.66   11.794%   $218.7361   $218.74   $218.75   $218.70  
  Purchase #3 $146.92   4.534%   $153.5814   $153.58   $153.60   $153.60  
  Purchase #4 $230.94   12.484%   $259.7705   $259.77   $259.75   $259.80  
  Purchase #5 $38.78   13.825%   $44.1413   $44.14   $44.15   $44.10  
  Purchase #6 $228.79   5.344%   $241.0165   $241.02   $241.00   $241.00  
  Purchase #7 $23.47   10.797%   $26.0041   $26.00   $26.00   $26.00  
  7 purchase totals = $910.18       $991.2449   $991.25   $991.25   $991.20