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 $75.70   13.113%   $85.6265   $85.63   $85.65   $85.60  
  Purchase #2 $217.37   13.187%   $246.0346   $246.03   $246.05   $246.00  
  Purchase #3 $21.86   7.348%   $23.4663   $23.47   $23.45   $23.50  
  Purchase #4 $41.69   13.638%   $47.3757   $47.38   $47.40   $47.40  
  Purchase #5 $223.41   4.743%   $234.0063   $234.01   $234.00   $234.00  
  Purchase #6 $173.94   12.594%   $195.846   $195.85   $195.85   $195.80  
  Purchase #7 $62.36   7.517%   $67.0476   $67.05   $67.05   $67.00  
  7 purchase totals = $816.33       $899.4030   $899.42   $899.45   $899.30