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 $57.34   8.766%   $62.3664   $62.37   $62.35   $62.40  
  Purchase #2 $206.74   10.547%   $228.5449   $228.54   $228.55   $228.50  
  Purchase #3 $85.65   9.703%   $93.9606   $93.96   $93.95   $94.00  
  Purchase #4 $41.83   10.755%   $46.3288   $46.33   $46.35   $46.30  
  Purchase #5 $23.82   10.201%   $26.2499   $26.25   $26.25   $26.20  
  Purchase #6 $233.95   4.187%   $243.7455   $243.75   $243.75   $243.70  
  Purchase #7 $65.70   8.427%   $71.2365   $71.24   $71.25   $71.20  
  7 purchase totals = $715.03       $772.4326   $772.44   $772.45   $772.30