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 $43.54   6.816%   $46.5077   $46.51   $46.50   $46.50  
  Purchase #2 $156.90   11.192%   $174.4602   $174.46   $174.45   $174.50  
  Purchase #3 $118.57   6.421%   $126.1834   $126.18   $126.20   $126.20  
  Purchase #4 $187.66   8.186%   $203.0218   $203.02   $203.00   $203.00  
  Purchase #5 $24.25   5.688%   $25.6293   $25.63   $25.65   $25.60  
  Purchase #6 $96.72   10.192%   $106.5777   $106.58   $106.60   $106.60  
  Purchase #7 $239.71   8.480%   $260.0374   $260.04   $260.05   $260.00  
  7 purchase totals = $867.35       $942.4175   $942.42   $942.45   $942.40