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 $184.79   3.827%   $191.8619   $191.86   $191.85   $191.90  
  Purchase #2 $93.47   10.425%   $103.2142   $103.21   $103.20   $103.20  
  Purchase #3 $225.88   8.239%   $244.4903   $244.49   $244.50   $244.50  
  Purchase #4 $208.80   13.649%   $237.2991   $237.30   $237.30   $237.30  
  Purchase #5 $137.68   7.723%   $148.313   $148.31   $148.30   $148.30  
  Purchase #6 $114.49   12.370%   $128.6524   $128.65   $128.65   $128.70  
  Purchase #7 $219.94   6.782%   $234.8563   $234.86   $234.85   $234.90  
  7 purchase totals = $1,185.05       $1,288.6872   $1,288.68   $1,288.65   $1,288.80