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 $56.82   9.538%   $62.2395   $62.24   $62.25   $62.20  
  Purchase #2 $157.30   11.231%   $174.9664   $174.97   $174.95   $175.00  
  Purchase #3 $239.39   12.213%   $268.6267   $268.63   $268.65   $268.60  
  Purchase #4 $25.68   11.409%   $28.6098   $28.61   $28.60   $28.60  
  Purchase #5 $179.65   4.487%   $187.7109   $187.71   $187.70   $187.70  
  Purchase #6 $156.42   4.664%   $163.7154   $163.72   $163.70   $163.70  
  Purchase #7 $175.25   12.784%   $197.654   $197.65   $197.65   $197.70  
  7 purchase totals = $990.51       $1,083.5227   $1,083.53   $1,083.50   $1,083.50