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 $185.43   13.524%   $210.5076   $210.51   $210.50   $210.50  
  Purchase #2 $186.97   7.749%   $201.4583   $201.46   $201.45   $201.50  
  Purchase #3 $140.63   12.814%   $158.6503   $158.65   $158.65   $158.70  
  Purchase #4 $248.45   8.771%   $270.2415   $270.24   $270.25   $270.20  
  Purchase #5 $58.89   9.815%   $64.6701   $64.67   $64.65   $64.70  
  Purchase #6 $175.68   13.199%   $198.868   $198.87   $198.85   $198.90  
  Purchase #7 $186.89   5.312%   $196.8176   $196.82   $196.80   $196.80  
  7 purchase totals = $1,182.94       $1,301.2134   $1,301.22   $1,301.15   $1,301.30