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 $151.63   5.273%   $159.6254   $159.63   $159.65   $159.60  
  Purchase #2 $179.39   8.128%   $193.9708   $193.97   $193.95   $194.00  
  Purchase #3 $102.87   8.583%   $111.6993   $111.70   $111.70   $111.70  
  Purchase #4 $136.52   7.361%   $146.5692   $146.57   $146.55   $146.60  
  Purchase #5 $240.63   4.806%   $252.1947   $252.19   $252.20   $252.20  
  Purchase #6 $63.32   6.285%   $67.2997   $67.30   $67.30   $67.30  
  Purchase #7 $107.79   10.444%   $119.0476   $119.05   $119.05   $119.00  
  7 purchase totals = $982.15       $1,050.4067   $1,050.41   $1,050.40   $1,050.40