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 $30.56   12.786%   $34.4674   $34.47   $34.45   $34.50  
  Purchase #2 $198.87   9.185%   $217.1362   $217.14   $217.15   $217.10  
  Purchase #3 $134.55   11.237%   $149.6694   $149.67   $149.65   $149.70  
  Purchase #4 $49.68   12.682%   $55.9804   $55.98   $56.00   $56.00  
  Purchase #5 $197.57   10.821%   $218.949   $218.95   $218.95   $218.90  
  Purchase #6 $205.69   11.432%   $229.2045   $229.20   $229.20   $229.20  
  Purchase #7 $153.36   5.729%   $162.146   $162.15   $162.15   $162.10  
  7 purchase totals = $970.28       $1,067.5529   $1,067.56   $1,067.55   $1,067.50