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 $61.97   5.280%   $65.242   $65.24   $65.25   $65.20  
  Purchase #2 $183.40   5.836%   $194.1032   $194.10   $194.10   $194.10  
  Purchase #3 $213.72   12.516%   $240.4692   $240.47   $240.45   $240.50  
  Purchase #4 $18.77   7.429%   $20.1644   $20.16   $20.15   $20.20  
  Purchase #5 $54.26   11.389%   $60.4397   $60.44   $60.45   $60.40  
  Purchase #6 $57.81   4.370%   $60.3363   $60.34   $60.35   $60.30  
  Purchase #7 $186.30   10.336%   $205.556   $205.56   $205.55   $205.60  
  7 purchase totals = $776.23       $846.3108   $846.31   $846.30   $846.30