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 $57.73   12.520%   $64.9578   $64.96   $64.95   $65.00  
  Purchase #2 $55.66   5.821%   $58.9   $58.90   $58.90   $58.90  
  Purchase #3 $229.71   4.682%   $240.465   $240.47   $240.45   $240.50  
  Purchase #4 $178.30   11.548%   $198.8901   $198.89   $198.90   $198.90  
  Purchase #5 $204.71   13.351%   $232.0408   $232.04   $232.05   $232.00  
  Purchase #6 $172.63   3.159%   $178.0834   $178.08   $178.10   $178.10  
  Purchase #7 $120.96   10.820%   $134.0479   $134.05   $134.05   $134.00  
  7 purchase totals = $1,019.70       $1,107.3850   $1,107.39   $1,107.40   $1,107.40