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 $53.92   10.506%   $59.5848   $59.58   $59.60   $59.60  
  Purchase #2 $116.61   6.541%   $124.2375   $124.24   $124.25   $124.20  
  Purchase #3 $56.37   3.618%   $58.4095   $58.41   $58.40   $58.40  
  Purchase #4 $24.58   11.715%   $27.4595   $27.46   $27.45   $27.50  
  Purchase #5 $69.70   13.824%   $79.3353   $79.34   $79.35   $79.30  
  Purchase #6 $171.84   10.617%   $190.0843   $190.08   $190.10   $190.10  
  Purchase #7 $201.39   9.693%   $220.9107   $220.91   $220.90   $220.90  
  7 purchase totals = $694.41       $760.0216   $760.02   $760.05   $760.00