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 $213.42   6.578%   $227.4588   $227.46   $227.45   $227.50  
  Purchase #2 $198.57   9.171%   $216.7809   $216.78   $216.80   $216.80  
  Purchase #3 $79.77   11.152%   $88.666   $88.67   $88.65   $88.70  
  Purchase #4 $57.89   13.475%   $65.6907   $65.69   $65.70   $65.70  
  Purchase #5 $146.95   4.605%   $153.717   $153.72   $153.70   $153.70  
  Purchase #6 $128.76   10.256%   $141.9656   $141.97   $141.95   $142.00  
  Purchase #7 $35.71   11.177%   $39.7013   $39.70   $39.70   $39.70  
  7 purchase totals = $861.07       $933.9803   $933.99   $933.95   $934.10