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 $52.58   13.228%   $59.5353   $59.54   $59.55   $59.50  
  Purchase #2 $234.78   7.252%   $251.8062   $251.81   $251.80   $251.80  
  Purchase #3 $95.59   12.761%   $107.7882   $107.79   $107.80   $107.80  
  Purchase #4 $202.42   9.485%   $221.6195   $221.62   $221.60   $221.60  
  Purchase #5 $157.27   4.167%   $163.8234   $163.82   $163.80   $163.80  
  Purchase #6 $92.50   13.815%   $105.2789   $105.28   $105.30   $105.30  
  Purchase #7 $188.82   11.348%   $210.2473   $210.25   $210.25   $210.20  
  7 purchase totals = $1,023.96       $1,120.0988   $1,120.11   $1,120.10   $1,120.00