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 $182.95   6.856%   $195.4931   $195.49   $195.50   $195.50  
  Purchase #2 $56.41   11.335%   $62.8041   $62.80   $62.80   $62.80  
  Purchase #3 $98.28   3.163%   $101.3886   $101.39   $101.40   $101.40  
  Purchase #4 $62.77   3.139%   $64.7404   $64.74   $64.75   $64.70  
  Purchase #5 $29.59   5.785%   $31.3018   $31.30   $31.30   $31.30  
  Purchase #6 $235.98   7.223%   $253.0248   $253.02   $253.00   $253.00  
  Purchase #7 $103.92   4.483%   $108.5787   $108.58   $108.60   $108.60  
  7 purchase totals = $769.90       $817.3315   $817.32   $817.35   $817.30