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 $69.27   10.327%   $76.4235   $76.42   $76.40   $76.40  
  Purchase #2 $224.61   10.531%   $248.2637   $248.26   $248.25   $248.30  
  Purchase #3 $213.88   8.643%   $232.3656   $232.37   $232.35   $232.40  
  Purchase #4 $94.88   7.721%   $102.2057   $102.21   $102.20   $102.20  
  Purchase #5 $159.92   3.203%   $165.0422   $165.04   $165.05   $165.00  
  Purchase #6 $162.66   10.676%   $180.0256   $180.03   $180.05   $180.00  
  Purchase #7 $46.52   8.803%   $50.6152   $50.62   $50.60   $50.60  
  7 purchase totals = $971.74       $1,054.9415   $1,054.95   $1,054.90   $1,054.90