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 $62.38   5.689%   $65.9288   $65.93   $65.95   $65.90  
  Purchase #2 $106.85   8.638%   $116.0797   $116.08   $116.10   $116.10  
  Purchase #3 $206.88   8.592%   $224.6551   $224.66   $224.65   $224.70  
  Purchase #4 $24.66   13.726%   $28.0448   $28.04   $28.05   $28.00  
  Purchase #5 $103.32   7.573%   $111.1444   $111.14   $111.15   $111.10  
  Purchase #6 $247.26   12.496%   $278.1576   $278.16   $278.15   $278.20  
  Purchase #7 $124.57   4.198%   $129.7994   $129.80   $129.80   $129.80  
  7 purchase totals = $875.92       $953.8098   $953.81   $953.85   $953.80