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 $239.30   9.739%   $262.6054   $262.61   $262.60   $262.60  
  Purchase #2 $142.52   10.851%   $157.9848   $157.98   $158.00   $158.00  
  Purchase #3 $43.52   12.391%   $48.9126   $48.91   $48.90   $48.90  
  Purchase #4 $133.46   10.206%   $147.0809   $147.08   $147.10   $147.10  
  Purchase #5 $148.59   5.380%   $156.5841   $156.58   $156.60   $156.60  
  Purchase #6 $205.43   5.272%   $216.2603   $216.26   $216.25   $216.30  
  Purchase #7 $128.53   5.295%   $135.3357   $135.34   $135.35   $135.30  
  7 purchase totals = $1,041.35       $1,124.7638   $1,124.76   $1,124.80   $1,124.80