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 $104.73   11.116%   $116.3718   $116.37   $116.35   $116.40  
  Purchase #2 $90.36   9.148%   $98.6261   $98.63   $98.65   $98.60  
  Purchase #3 $144.73   10.824%   $160.3956   $160.40   $160.40   $160.40  
  Purchase #4 $203.58   8.607%   $221.1021   $221.10   $221.10   $221.10  
  Purchase #5 $184.43   10.441%   $203.6863   $203.69   $203.70   $203.70  
  Purchase #6 $197.76   12.548%   $222.5749   $222.57   $222.55   $222.60  
  Purchase #7 $129.87   10.721%   $143.7934   $143.79   $143.80   $143.80  
  7 purchase totals = $1,055.46       $1,166.5502   $1,166.55   $1,166.55   $1,166.60