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 $216.63   8.759%   $235.6046   $235.60   $235.60   $235.60  
  Purchase #2 $139.35   7.593%   $149.9308   $149.93   $149.95   $149.90  
  Purchase #3 $156.79   4.301%   $163.5335   $163.53   $163.55   $163.50  
  Purchase #4 $81.27   4.445%   $84.8825   $84.88   $84.90   $84.90  
  Purchase #5 $34.82   9.444%   $38.1084   $38.11   $38.10   $38.10  
  Purchase #6 $74.94   9.540%   $82.0893   $82.09   $82.10   $82.10  
  Purchase #7 $162.34   10.861%   $179.9717   $179.97   $179.95   $180.00  
  7 purchase totals = $866.14       $934.1208   $934.11   $934.15   $934.10