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 $142.65   4.663%   $149.3018   $149.30   $149.30   $149.30  
  Purchase #2 $203.80   12.840%   $229.9679   $229.97   $229.95   $230.00  
  Purchase #3 $16.26   3.678%   $16.858   $16.86   $16.85   $16.90  
  Purchase #4 $54.83   10.621%   $60.6535   $60.65   $60.65   $60.70  
  Purchase #5 $171.35   3.420%   $177.2102   $177.21   $177.20   $177.20  
  Purchase #6 $228.42   12.191%   $256.2667   $256.27   $256.25   $256.30  
  Purchase #7 $163.28   8.266%   $176.7767   $176.78   $176.80   $176.80  
  7 purchase totals = $980.59       $1,067.0348   $1,067.04   $1,067.00   $1,067.20