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 $53.71   11.651%   $59.9678   $59.97   $59.95   $60.00  
  Purchase #2 $140.49   5.224%   $147.8292   $147.83   $147.85   $147.80  
  Purchase #3 $14.40   9.512%   $15.7697   $15.77   $15.75   $15.80  
  Purchase #4 $36.57   10.171%   $40.2895   $40.29   $40.30   $40.30  
  Purchase #5 $168.58   9.462%   $184.531   $184.53   $184.55   $184.50  
  Purchase #6 $109.60   4.734%   $114.7885   $114.79   $114.80   $114.80  
  Purchase #7 $182.77   11.474%   $203.741   $203.74   $203.75   $203.70  
  7 purchase totals = $706.12       $766.9167   $766.92   $766.95   $766.90