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 $136.63   11.806%   $152.7605   $152.76   $152.75   $152.80  
  Purchase #2 $78.65   9.466%   $86.095   $86.10   $86.10   $86.10  
  Purchase #3 $175.77   9.714%   $192.8443   $192.84   $192.85   $192.80  
  Purchase #4 $75.36   10.264%   $83.095   $83.10   $83.10   $83.10  
  Purchase #5 $57.58   3.159%   $59.399   $59.40   $59.40   $59.40  
  Purchase #6 $22.76   13.297%   $25.7864   $25.79   $25.80   $25.80  
  Purchase #7 $184.91   13.587%   $210.0337   $210.03   $210.05   $210.00  
  7 purchase totals = $731.66       $810.0139   $810.02   $810.05   $810.00