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 $147.31   12.361%   $165.519   $165.52   $165.50   $165.50  
  Purchase #2 $206.58   9.809%   $226.8434   $226.84   $226.85   $226.80  
  Purchase #3 $107.38   10.455%   $118.6066   $118.61   $118.60   $118.60  
  Purchase #4 $84.38   6.576%   $89.9288   $89.93   $89.95   $89.90  
  Purchase #5 $67.47   10.358%   $74.4585   $74.46   $74.45   $74.50  
  Purchase #6 $15.66   4.263%   $16.3276   $16.33   $16.35   $16.30  
  Purchase #7 $104.28   7.613%   $112.2188   $112.22   $112.20   $112.20  
  7 purchase totals = $733.06       $803.9027   $803.91   $803.90   $803.80