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 $246.35   8.274%   $266.733   $266.73   $266.75   $266.70  
  Purchase #2 $74.90   8.123%   $80.9841   $80.98   $81.00   $81.00  
  Purchase #3 $53.89   11.364%   $60.0141   $60.01   $60.00   $60.00  
  Purchase #4 $180.36   10.355%   $199.0363   $199.04   $199.05   $199.00  
  Purchase #5 $56.65   5.811%   $59.9419   $59.94   $59.95   $59.90  
  Purchase #6 $249.40   5.713%   $263.6482   $263.65   $263.65   $263.60  
  Purchase #7 $71.41   6.787%   $76.2566   $76.26   $76.25   $76.30  
  7 purchase totals = $932.96       $1,006.6142   $1,006.61   $1,006.65   $1,006.50