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 $56.47   5.824%   $59.7588   $59.76   $59.75   $59.80  
  Purchase #2 $227.76   12.210%   $255.5695   $255.57   $255.55   $255.60  
  Purchase #3 $69.68   7.585%   $74.9652   $74.97   $74.95   $75.00  
  Purchase #4 $232.41   13.761%   $264.3919   $264.39   $264.40   $264.40  
  Purchase #5 $35.55   4.159%   $37.0285   $37.03   $37.05   $37.00  
  Purchase #6 $147.44   10.131%   $162.3771   $162.38   $162.40   $162.40  
  Purchase #7 $239.59   5.162%   $251.9576   $251.96   $251.95   $252.00  
  7 purchase totals = $1,008.90       $1,106.0486   $1,106.06   $1,106.05   $1,106.20