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 $226.27   9.432%   $247.6118   $247.61   $247.60   $247.60  
  Purchase #2 $119.80   3.697%   $124.229   $124.23   $124.25   $124.20  
  Purchase #3 $180.95   5.203%   $190.3648   $190.36   $190.35   $190.40  
  Purchase #4 $17.56   8.830%   $19.1105   $19.11   $19.10   $19.10  
  Purchase #5 $175.48   11.611%   $195.855   $195.86   $195.85   $195.90  
  Purchase #6 $101.78   11.780%   $113.7697   $113.77   $113.75   $113.80  
  Purchase #7 $81.47   3.822%   $84.5838   $84.58   $84.60   $84.60  
  7 purchase totals = $903.31       $975.5246   $975.52   $975.50   $975.60