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 $60.42   13.769%   $68.7392   $68.74   $68.75   $68.70  
  Purchase #2 $114.94   3.302%   $118.7353   $118.74   $118.75   $118.70  
  Purchase #3 $17.67   5.495%   $18.641   $18.64   $18.65   $18.60  
  Purchase #4 $227.45   9.192%   $248.3572   $248.36   $248.35   $248.40  
  Purchase #5 $67.60   11.130%   $75.1239   $75.12   $75.10   $75.10  
  Purchase #6 $203.95   10.242%   $224.8386   $224.84   $224.85   $224.80  
  Purchase #7 $84.86   13.441%   $96.266   $96.27   $96.25   $96.30  
  7 purchase totals = $776.89       $850.7012   $850.71   $850.70   $850.60