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 $237.73   10.871%   $263.5736   $263.57   $263.55   $263.60  
  Purchase #2 $50.31   11.411%   $56.0509   $56.05   $56.05   $56.10  
  Purchase #3 $90.37   3.376%   $93.4209   $93.42   $93.40   $93.40  
  Purchase #4 $150.96   6.406%   $160.6305   $160.63   $160.65   $160.60  
  Purchase #5 $97.73   9.827%   $107.3339   $107.33   $107.35   $107.30  
  Purchase #6 $188.28   11.326%   $209.6046   $209.60   $209.60   $209.60  
  Purchase #7 $114.87   10.237%   $126.6292   $126.63   $126.65   $126.60  
  7 purchase totals = $930.25       $1,017.2436   $1,017.23   $1,017.25   $1,017.20