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 $153.84   13.723%   $174.9515   $174.95   $174.95   $175.00  
  Purchase #2 $210.48   4.384%   $219.7074   $219.71   $219.70   $219.70  
  Purchase #3 $97.51   12.425%   $109.6256   $109.63   $109.65   $109.60  
  Purchase #4 $180.93   8.703%   $196.6763   $196.68   $196.70   $196.70  
  Purchase #5 $60.91   4.432%   $63.6095   $63.61   $63.60   $63.60  
  Purchase #6 $156.42   4.806%   $163.9375   $163.94   $163.95   $163.90  
  Purchase #7 $64.53   5.482%   $68.0675   $68.07   $68.05   $68.10  
  7 purchase totals = $924.62       $996.5753   $996.59   $996.60   $996.60