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 $163.89   12.434%   $184.2681   $184.27   $184.25   $184.30  
  Purchase #2 $229.67   10.485%   $253.7509   $253.75   $253.75   $253.80  
  Purchase #3 $13.77   8.240%   $14.9046   $14.90   $14.90   $14.90  
  Purchase #4 $215.28   10.492%   $237.8672   $237.87   $237.85   $237.90  
  Purchase #5 $119.49   11.816%   $133.6089   $133.61   $133.60   $133.60  
  Purchase #6 $195.48   7.143%   $209.4431   $209.44   $209.45   $209.40  
  Purchase #7 $58.53   5.206%   $61.5771   $61.58   $61.60   $61.60  
  7 purchase totals = $996.11       $1,095.4199   $1,095.42   $1,095.40   $1,095.50