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 $56.67   10.147%   $62.4203   $62.42   $62.40   $62.40  
  Purchase #2 $174.34   12.740%   $196.5509   $196.55   $196.55   $196.60  
  Purchase #3 $177.30   3.289%   $183.1314   $183.13   $183.15   $183.10  
  Purchase #4 $204.46   9.834%   $224.5666   $224.57   $224.55   $224.60  
  Purchase #5 $249.60   9.407%   $273.0799   $273.08   $273.10   $273.10  
  Purchase #6 $150.97   7.710%   $162.6098   $162.61   $162.60   $162.60  
  Purchase #7 $246.63   3.652%   $255.6369   $255.64   $255.65   $255.60  
  7 purchase totals = $1,259.97       $1,357.9958   $1,358.00   $1,358.00   $1,358.00