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 $103.57   13.723%   $117.7829   $117.78   $117.80   $117.80  
  Purchase #2 $179.32   10.304%   $197.7971   $197.80   $197.80   $197.80  
  Purchase #3 $107.26   11.718%   $119.8287   $119.83   $119.85   $119.80  
  Purchase #4 $151.59   5.237%   $159.5288   $159.53   $159.55   $159.50  
  Purchase #5 $177.55   4.801%   $186.0742   $186.07   $186.05   $186.10  
  Purchase #6 $35.82   12.829%   $40.4153   $40.42   $40.40   $40.40  
  Purchase #7 $119.95   9.354%   $131.1701   $131.17   $131.15   $131.20  
  7 purchase totals = $875.06       $952.5971   $952.60   $952.60   $952.60