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 $55.68   8.178%   $60.2335   $60.23   $60.25   $60.20  
  Purchase #2 $106.34   6.820%   $113.5924   $113.59   $113.60   $113.60  
  Purchase #3 $113.52   12.213%   $127.3842   $127.38   $127.40   $127.40  
  Purchase #4 $221.31   6.703%   $236.1444   $236.14   $236.15   $236.10  
  Purchase #5 $95.95   13.686%   $109.0817   $109.08   $109.10   $109.10  
  Purchase #6 $38.90   4.758%   $40.7509   $40.75   $40.75   $40.80  
  Purchase #7 $235.90   4.616%   $246.7891   $246.79   $246.80   $246.80  
  7 purchase totals = $867.60       $933.9762   $933.96   $934.05   $934.00