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 $174.89   13.400%   $198.3253   $198.33   $198.35   $198.30  
  Purchase #2 $108.59   10.202%   $119.6684   $119.67   $119.65   $119.70  
  Purchase #3 $186.85   12.858%   $210.8752   $210.88   $210.90   $210.90  
  Purchase #4 $66.28   11.619%   $73.9811   $73.98   $74.00   $74.00  
  Purchase #5 $117.98   13.611%   $134.0383   $134.04   $134.05   $134.00  
  Purchase #6 $83.48   5.748%   $88.2784   $88.28   $88.30   $88.30  
  Purchase #7 $220.93   12.404%   $248.3342   $248.33   $248.35   $248.30  
  7 purchase totals = $959.00       $1,073.5009   $1,073.51   $1,073.60   $1,073.50