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 $116.94   6.393%   $124.416   $124.42   $124.40   $124.40  
  Purchase #2 $168.84   5.307%   $177.8003   $177.80   $177.80   $177.80  
  Purchase #3 $21.76   10.128%   $23.9639   $23.96   $23.95   $24.00  
  Purchase #4 $36.89   6.542%   $39.3033   $39.30   $39.30   $39.30  
  Purchase #5 $74.73   3.464%   $77.3186   $77.32   $77.30   $77.30  
  Purchase #6 $239.93   5.836%   $253.9323   $253.93   $253.95   $253.90  
  Purchase #7 $113.95   11.658%   $127.2343   $127.23   $127.25   $127.20  
  7 purchase totals = $773.04       $823.9687   $823.96   $823.95   $823.90