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 $148.66   12.787%   $167.6692   $167.67   $167.65   $167.70  
  Purchase #2 $5.67   12.681%   $6.389   $6.39   $6.40   $6.40  
  Purchase #3 $66.66   12.129%   $74.7452   $74.75   $74.75   $74.70  
  Purchase #4 $37.36   12.169%   $41.9063   $41.91   $41.90   $41.90  
  Purchase #5 $168.96   4.172%   $176.009   $176.01   $176.00   $176.00  
  Purchase #6 $42.46   12.462%   $47.7514   $47.75   $47.75   $47.80  
  Purchase #7 $197.70   7.470%   $212.4682   $212.47   $212.45   $212.50  
  7 purchase totals = $667.47       $726.9383   $726.95   $726.90   $727.00