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 $93.41   5.581%   $98.6232   $98.62   $98.60   $98.60  
  Purchase #2 $119.31   13.811%   $135.7879   $135.79   $135.80   $135.80  
  Purchase #3 $187.56   5.756%   $198.356   $198.36   $198.35   $198.40  
  Purchase #4 $193.56   4.492%   $202.2547   $202.25   $202.25   $202.30  
  Purchase #5 $172.35   13.184%   $195.0726   $195.07   $195.05   $195.10  
  Purchase #6 $179.84   7.349%   $193.0564   $193.06   $193.05   $193.10  
  Purchase #7 $88.55   11.387%   $98.6332   $98.63   $98.65   $98.60  
  7 purchase totals = $1,034.58       $1,121.7840   $1,121.78   $1,121.75   $1,121.90