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 $150.66   11.775%   $168.4002   $168.40   $168.40   $168.40  
  Purchase #2 $156.47   3.647%   $162.1765   $162.18   $162.20   $162.20  
  Purchase #3 $66.78   10.591%   $73.8527   $73.85   $73.85   $73.90  
  Purchase #4 $234.92   3.128%   $242.2683   $242.27   $242.25   $242.30  
  Purchase #5 $145.90   10.231%   $160.827   $160.83   $160.85   $160.80  
  Purchase #6 $230.96   12.725%   $260.3497   $260.35   $260.35   $260.30  
  Purchase #7 $181.27   9.429%   $198.3619   $198.36   $198.35   $198.40  
  7 purchase totals = $1,166.96       $1,266.2363   $1,266.24   $1,266.25   $1,266.30