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 $229.49   5.531%   $242.1831   $242.18   $242.20   $242.20  
  Purchase #2 $13.86   13.137%   $15.6808   $15.68   $15.70   $15.70  
  Purchase #3 $238.85   3.763%   $247.8379   $247.84   $247.85   $247.80  
  Purchase #4 $142.87   5.153%   $150.2321   $150.23   $150.25   $150.20  
  Purchase #5 $234.35   4.320%   $244.4739   $244.47   $244.45   $244.50  
  Purchase #6 $25.36   11.143%   $28.1859   $28.19   $28.20   $28.20  
  Purchase #7 $114.90   8.665%   $124.8561   $124.86   $124.85   $124.90  
  7 purchase totals = $999.68       $1,053.4498   $1,053.45   $1,053.50   $1,053.50