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 $232.26   13.162%   $262.8301   $262.83   $262.85   $262.80  
  Purchase #2 $137.93   12.865%   $155.6747   $155.67   $155.65   $155.70  
  Purchase #3 $147.30   10.300%   $162.4719   $162.47   $162.45   $162.50  
  Purchase #4 $22.51   8.510%   $24.4256   $24.43   $24.45   $24.40  
  Purchase #5 $157.81   11.228%   $175.5289   $175.53   $175.55   $175.50  
  Purchase #6 $108.87   12.555%   $122.5386   $122.54   $122.55   $122.50  
  Purchase #7 $189.90   5.164%   $199.7064   $199.71   $199.70   $199.70  
  7 purchase totals = $996.58       $1,103.1762   $1,103.18   $1,103.20   $1,103.10