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 $31.34   5.542%   $33.0769   $33.08   $33.10   $33.10  
  Purchase #2 $211.58   3.426%   $218.8287   $218.83   $218.85   $218.80  
  Purchase #3 $116.66   12.115%   $130.7934   $130.79   $130.80   $130.80  
  Purchase #4 $163.89   11.645%   $182.975   $182.98   $183.00   $183.00  
  Purchase #5 $10.51   10.628%   $11.627   $11.63   $11.65   $11.60  
  Purchase #6 $223.49   5.825%   $236.5083   $236.51   $236.50   $236.50  
  Purchase #7 $136.60   8.131%   $147.7069   $147.71   $147.70   $147.70  
  7 purchase totals = $894.07       $961.5162   $961.53   $961.60   $961.50