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 $204.89   5.362%   $215.8762   $215.88   $215.90   $215.90  
  Purchase #2 $211.54   5.855%   $223.9257   $223.93   $223.95   $223.90  
  Purchase #3 $142.61   12.577%   $160.5461   $160.55   $160.55   $160.50  
  Purchase #4 $249.99   9.599%   $273.9865   $273.99   $274.00   $274.00  
  Purchase #5 $223.94   11.615%   $249.9506   $249.95   $249.95   $250.00  
  Purchase #6 $72.76   6.329%   $77.365   $77.37   $77.35   $77.40  
  Purchase #7 $54.37   12.204%   $61.0053   $61.01   $61.00   $61.00  
  7 purchase totals = $1,160.10       $1,262.6554   $1,262.68   $1,262.70   $1,262.70