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 $72.58   5.739%   $76.7454   $76.75   $76.75   $76.70  
  Purchase #2 $238.73   3.730%   $247.6346   $247.63   $247.65   $247.60  
  Purchase #3 $248.91   5.844%   $263.4563   $263.46   $263.45   $263.50  
  Purchase #4 $190.41   9.153%   $207.8382   $207.84   $207.85   $207.80  
  Purchase #5 $234.27   9.376%   $256.2352   $256.24   $256.25   $256.20  
  Purchase #6 $116.30   8.791%   $126.5239   $126.52   $126.50   $126.50  
  Purchase #7 $51.72   3.637%   $53.6011   $53.60   $53.60   $53.60  
  7 purchase totals = $1,152.92       $1,232.0347   $1,232.04   $1,232.05   $1,231.90