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 $139.59   13.865%   $158.9442   $158.94   $158.95   $158.90  
  Purchase #2 $166.59   12.135%   $186.8057   $186.81   $186.80   $186.80  
  Purchase #3 $212.62   9.231%   $232.247   $232.25   $232.25   $232.20  
  Purchase #4 $191.54   6.744%   $204.4575   $204.46   $204.45   $204.50  
  Purchase #5 $90.25   12.277%   $101.33   $101.33   $101.35   $101.30  
  Purchase #6 $234.83   6.662%   $250.4744   $250.47   $250.45   $250.50  
  Purchase #7 $60.94   3.302%   $62.9522   $62.95   $62.95   $63.00  
  7 purchase totals = $1,096.36       $1,197.2110   $1,197.21   $1,197.20   $1,197.20