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 $206.45   4.513%   $215.7671   $215.77   $215.75   $215.80  
  Purchase #2 $222.26   3.786%   $230.6748   $230.67   $230.65   $230.70  
  Purchase #3 $221.27   4.394%   $230.9926   $230.99   $231.00   $231.00  
  Purchase #4 $78.86   11.774%   $88.145   $88.15   $88.15   $88.10  
  Purchase #5 $230.27   11.450%   $256.6359   $256.64   $256.65   $256.60  
  Purchase #6 $114.36   4.331%   $119.3129   $119.31   $119.30   $119.30  
  Purchase #7 $144.36   11.300%   $160.6727   $160.67   $160.65   $160.70  
  7 purchase totals = $1,217.83       $1,302.2010   $1,302.20   $1,302.15   $1,302.20