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 $60.67   4.803%   $63.584   $63.58   $63.60   $63.60  
  Purchase #2 $66.48   3.501%   $68.8075   $68.81   $68.80   $68.80  
  Purchase #3 $17.85   12.618%   $20.1023   $20.10   $20.10   $20.10  
  Purchase #4 $248.57   12.351%   $279.2709   $279.27   $279.25   $279.30  
  Purchase #5 $244.42   10.705%   $270.5852   $270.59   $270.60   $270.60  
  Purchase #6 $32.43   8.253%   $35.1064   $35.11   $35.10   $35.10  
  Purchase #7 $95.86   10.625%   $106.0451   $106.05   $106.05   $106.00  
  7 purchase totals = $766.28       $843.5014   $843.51   $843.50   $843.50