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 $153.41   6.534%   $163.4338   $163.43   $163.45   $163.40  
  Purchase #2 $62.25   3.119%   $64.1916   $64.19   $64.20   $64.20  
  Purchase #3 $176.70   7.722%   $190.3448   $190.34   $190.35   $190.30  
  Purchase #4 $240.78   5.748%   $254.62   $254.62   $254.60   $254.60  
  Purchase #5 $227.99   11.804%   $254.9019   $254.90   $254.90   $254.90  
  Purchase #6 $57.81   12.516%   $65.0455   $65.05   $65.05   $65.00  
  Purchase #7 $241.46   9.146%   $263.5439   $263.54   $263.55   $263.50  
  7 purchase totals = $1,160.40       $1,256.0815   $1,256.07   $1,256.10   $1,255.90