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 $223.78   10.621%   $247.5477   $247.55   $247.55   $247.50  
  Purchase #2 $77.52   8.858%   $84.3867   $84.39   $84.40   $84.40  
  Purchase #3 $149.84   10.726%   $165.9118   $165.91   $165.90   $165.90  
  Purchase #4 $110.61   12.830%   $124.8013   $124.80   $124.80   $124.80  
  Purchase #5 $237.46   8.869%   $258.5203   $258.52   $258.50   $258.50  
  Purchase #6 $182.90   12.241%   $205.2888   $205.29   $205.30   $205.30  
  Purchase #7 $16.44   11.618%   $18.35   $18.35   $18.35   $18.40  
  7 purchase totals = $998.55       $1,104.8066   $1,104.81   $1,104.80   $1,104.80