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 $189.94   11.294%   $211.3918   $211.39   $211.40   $211.40  
  Purchase #2 $16.78   6.403%   $17.8544   $17.85   $17.85   $17.90  
  Purchase #3 $182.63   3.307%   $188.6696   $188.67   $188.65   $188.70  
  Purchase #4 $57.46   5.698%   $60.7341   $60.73   $60.75   $60.70  
  Purchase #5 $14.54   12.153%   $16.307   $16.31   $16.30   $16.30  
  Purchase #6 $140.74   4.805%   $147.5026   $147.50   $147.50   $147.50  
  Purchase #7 $102.58   13.832%   $116.7689   $116.77   $116.75   $116.80  
  7 purchase totals = $704.67       $759.2284   $759.22   $759.20   $759.30