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 $58.41   8.338%   $63.2802   $63.28   $63.30   $63.30  
  Purchase #2 $70.67   11.670%   $78.9172   $78.92   $78.90   $78.90  
  Purchase #3 $94.34   11.575%   $105.2599   $105.26   $105.25   $105.30  
  Purchase #4 $53.58   12.795%   $60.4356   $60.44   $60.45   $60.40  
  Purchase #5 $110.68   7.565%   $119.0529   $119.05   $119.05   $119.10  
  Purchase #6 $138.49   8.548%   $150.3281   $150.33   $150.35   $150.30  
  Purchase #7 $174.93   4.486%   $182.7774   $182.78   $182.80   $182.80  
  7 purchase totals = $701.10       $760.0513   $760.06   $760.10   $760.10