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 $111.52   13.241%   $126.2864   $126.29   $126.30   $126.30  
  Purchase #2 $22.81   3.563%   $23.6227   $23.62   $23.60   $23.60  
  Purchase #3 $65.83   12.435%   $74.016   $74.02   $74.00   $74.00  
  Purchase #4 $33.52   8.746%   $36.4517   $36.45   $36.45   $36.50  
  Purchase #5 $112.31   7.519%   $120.7546   $120.75   $120.75   $120.80  
  Purchase #6 $105.79   12.626%   $119.147   $119.15   $119.15   $119.10  
  Purchase #7 $155.70   4.305%   $162.4029   $162.40   $162.40   $162.40  
  7 purchase totals = $607.48       $662.6813   $662.68   $662.65   $662.70