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 $175.73   10.713%   $194.556   $194.56   $194.55   $194.60  
  Purchase #2 $209.49   6.303%   $222.6942   $222.69   $222.70   $222.70  
  Purchase #3 $188.62   12.181%   $211.5958   $211.60   $211.60   $211.60  
  Purchase #4 $63.41   7.163%   $67.9521   $67.95   $67.95   $68.00  
  Purchase #5 $77.52   11.476%   $86.4162   $86.42   $86.40   $86.40  
  Purchase #6 $107.96   10.510%   $119.3066   $119.31   $119.30   $119.30  
  Purchase #7 $100.27   12.684%   $112.9882   $112.99   $113.00   $113.00  
  7 purchase totals = $923.00       $1,015.5091   $1,015.52   $1,015.50   $1,015.60