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 $205.65   10.483%   $227.2083   $227.21   $227.20   $227.20  
  Purchase #2 $44.59   10.233%   $49.1529   $49.15   $49.15   $49.20  
  Purchase #3 $165.91   7.465%   $178.2952   $178.30   $178.30   $178.30  
  Purchase #4 $66.62   12.358%   $74.8529   $74.85   $74.85   $74.90  
  Purchase #5 $225.45   3.581%   $233.5234   $233.52   $233.50   $233.50  
  Purchase #6 $59.90   9.542%   $65.6157   $65.62   $65.60   $65.60  
  Purchase #7 $97.77   3.412%   $101.1059   $101.11   $101.10   $101.10  
  7 purchase totals = $865.89       $929.7543   $929.76   $929.70   $929.80