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 $186.79   4.287%   $194.7977   $194.80   $194.80   $194.80  
  Purchase #2 $207.50   11.596%   $231.5617   $231.56   $231.55   $231.60  
  Purchase #3 $70.53   4.253%   $73.5296   $73.53   $73.55   $73.50  
  Purchase #4 $175.92   4.427%   $183.708   $183.71   $183.70   $183.70  
  Purchase #5 $229.95   10.551%   $254.212   $254.21   $254.20   $254.20  
  Purchase #6 $110.77   12.778%   $124.9242   $124.92   $124.90   $124.90  
  Purchase #7 $170.55   10.264%   $188.0553   $188.06   $188.05   $188.10  
  7 purchase totals = $1,152.01       $1,250.7885   $1,250.79   $1,250.75   $1,250.80