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 $59.71   11.527%   $66.5928   $66.59   $66.60   $66.60  
  Purchase #2 $192.65   3.629%   $199.6413   $199.64   $199.65   $199.60  
  Purchase #3 $30.49   10.855%   $33.7997   $33.80   $33.80   $33.80  
  Purchase #4 $144.87   12.228%   $162.5847   $162.58   $162.60   $162.60  
  Purchase #5 $231.26   3.327%   $238.954   $238.95   $238.95   $239.00  
  Purchase #6 $93.37   3.255%   $96.4092   $96.41   $96.40   $96.40  
  Purchase #7 $124.29   10.507%   $137.3492   $137.35   $137.35   $137.30  
  7 purchase totals = $876.64       $935.3309   $935.32   $935.35   $935.30