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 $248.73   11.196%   $276.5778   $276.58   $276.60   $276.60  
  Purchase #2 $102.50   13.205%   $116.0351   $116.04   $116.05   $116.00  
  Purchase #3 $51.82   13.267%   $58.695   $58.70   $58.70   $58.70  
  Purchase #4 $62.56   4.433%   $65.3333   $65.33   $65.35   $65.30  
  Purchase #5 $235.27   8.386%   $254.9997   $255.00   $255.00   $255.00  
  Purchase #6 $104.84   4.482%   $109.5389   $109.54   $109.55   $109.50  
  Purchase #7 $174.27   5.601%   $184.0309   $184.03   $184.05   $184.00  
  7 purchase totals = $979.99       $1,065.2107   $1,065.22   $1,065.30   $1,065.10