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 $96.85   4.842%   $101.5395   $101.54   $101.55   $101.50  
  Purchase #2 $113.37   10.582%   $125.3668   $125.37   $125.35   $125.40  
  Purchase #3 $180.47   13.304%   $204.4797   $204.48   $204.50   $204.50  
  Purchase #4 $64.68   5.221%   $68.0569   $68.06   $68.05   $68.10  
  Purchase #5 $102.58   11.668%   $114.549   $114.55   $114.55   $114.50  
  Purchase #6 $154.91   8.514%   $168.099   $168.10   $168.10   $168.10  
  Purchase #7 $69.75   7.849%   $75.2247   $75.22   $75.20   $75.20  
  7 purchase totals = $782.61       $857.3156   $857.32   $857.30   $857.30