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 $208.60   12.361%   $234.385   $234.39   $234.40   $234.40  
  Purchase #2 $62.55   4.400%   $65.3022   $65.30   $65.30   $65.30  
  Purchase #3 $94.61   7.756%   $101.948   $101.95   $101.95   $101.90  
  Purchase #4 $201.71   11.740%   $225.3908   $225.39   $225.40   $225.40  
  Purchase #5 $80.55   6.465%   $85.7576   $85.76   $85.75   $85.80  
  Purchase #6 $55.84   7.794%   $60.1922   $60.19   $60.20   $60.20  
  Purchase #7 $123.91   8.743%   $134.7435   $134.74   $134.75   $134.70  
  7 purchase totals = $827.77       $907.7193   $907.72   $907.75   $907.70