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 $160.84   9.849%   $176.6811   $176.68   $176.70   $176.70  
  Purchase #2 $206.92   4.153%   $215.5134   $215.51   $215.50   $215.50  
  Purchase #3 $126.88   12.388%   $142.5979   $142.60   $142.60   $142.60  
  Purchase #4 $210.87   12.277%   $236.7585   $236.76   $236.75   $236.80  
  Purchase #5 $105.57   10.827%   $117.0001   $117.00   $117.00   $117.00  
  Purchase #6 $46.76   11.544%   $52.158   $52.16   $52.15   $52.20  
  Purchase #7 $233.72   8.272%   $253.0533   $253.05   $253.05   $253.10  
  7 purchase totals = $1,091.56       $1,193.7623   $1,193.76   $1,193.75   $1,193.90