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 $210.38   7.668%   $226.5119   $226.51   $226.50   $226.50  
  Purchase #2 $119.99   10.801%   $132.9501   $132.95   $132.95   $133.00  
  Purchase #3 $147.58   6.493%   $157.1624   $157.16   $157.15   $157.20  
  Purchase #4 $94.76   13.293%   $107.3564   $107.36   $107.35   $107.40  
  Purchase #5 $84.42   10.717%   $93.4673   $93.47   $93.45   $93.50  
  Purchase #6 $174.71   10.835%   $193.6398   $193.64   $193.65   $193.60  
  Purchase #7 $60.32   8.613%   $65.5154   $65.52   $65.50   $65.50  
  7 purchase totals = $892.16       $976.6033   $976.61   $976.55   $976.70