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 $163.91   13.789%   $186.5115   $186.51   $186.50   $186.50  
  Purchase #2 $60.35   3.706%   $62.5866   $62.59   $62.60   $62.60  
  Purchase #3 $179.42   4.545%   $187.5746   $187.57   $187.55   $187.60  
  Purchase #4 $48.94   10.429%   $54.044   $54.04   $54.05   $54.00  
  Purchase #5 $190.63   10.515%   $210.6747   $210.67   $210.65   $210.70  
  Purchase #6 $211.80   11.858%   $236.9152   $236.92   $236.90   $236.90  
  Purchase #7 $106.37   7.548%   $114.3988   $114.40   $114.40   $114.40  
  7 purchase totals = $961.42       $1,052.7054   $1,052.70   $1,052.65   $1,052.70