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 $34.34   8.162%   $37.1428   $37.14   $37.15   $37.10  
  Purchase #2 $119.75   5.560%   $126.4081   $126.41   $126.40   $126.40  
  Purchase #3 $133.53   5.599%   $141.0063   $141.01   $141.00   $141.00  
  Purchase #4 $127.58   10.543%   $141.0308   $141.03   $141.05   $141.00  
  Purchase #5 $228.79   11.777%   $255.7346   $255.73   $255.75   $255.70  
  Purchase #6 $181.37   12.600%   $204.2226   $204.22   $204.20   $204.20  
  Purchase #7 $56.74   6.556%   $60.4599   $60.46   $60.45   $60.50  
  7 purchase totals = $882.10       $966.0051   $966.00   $966.00   $965.90