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 $176.56   8.872%   $192.2244   $192.22   $192.20   $192.20  
  Purchase #2 $241.40   9.261%   $263.7561   $263.76   $263.75   $263.80  
  Purchase #3 $136.91   3.171%   $141.2514   $141.25   $141.25   $141.30  
  Purchase #4 $232.36   11.369%   $258.777   $258.78   $258.80   $258.80  
  Purchase #5 $60.57   3.232%   $62.5276   $62.53   $62.55   $62.50  
  Purchase #6 $49.59   5.432%   $52.2837   $52.28   $52.30   $52.30  
  Purchase #7 $233.88   13.152%   $264.6399   $264.64   $264.65   $264.60  
  7 purchase totals = $1,131.27       $1,235.4601   $1,235.46   $1,235.50   $1,235.50