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 $211.49   8.742%   $229.9785   $229.98   $230.00   $230.00  
  Purchase #2 $119.79   12.387%   $134.6284   $134.63   $134.65   $134.60  
  Purchase #3 $166.53   10.462%   $183.9524   $183.95   $183.95   $184.00  
  Purchase #4 $68.90   5.571%   $72.7384   $72.74   $72.75   $72.70  
  Purchase #5 $238.93   5.713%   $252.5801   $252.58   $252.60   $252.60  
  Purchase #6 $174.64   13.843%   $198.8154   $198.82   $198.80   $198.80  
  Purchase #7 $246.37   7.310%   $264.3796   $264.38   $264.40   $264.40  
  7 purchase totals = $1,226.65       $1,337.0728   $1,337.08   $1,337.15   $1,337.10