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 $168.63   10.440%   $186.235   $186.24   $186.25   $186.20  
  Purchase #2 $88.31   5.548%   $93.2094   $93.21   $93.20   $93.20  
  Purchase #3 $156.96   7.301%   $168.4196   $168.42   $168.40   $168.40  
  Purchase #4 $213.82   5.492%   $225.563   $225.56   $225.55   $225.60  
  Purchase #5 $196.98   6.399%   $209.5848   $209.58   $209.60   $209.60  
  Purchase #6 $42.68   10.822%   $47.2988   $47.30   $47.30   $47.30  
  Purchase #7 $186.81   12.681%   $210.4994   $210.50   $210.50   $210.50  
  7 purchase totals = $1,054.19       $1,140.8100   $1,140.81   $1,140.80   $1,140.80