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 $246.86   13.295%   $279.68   $279.68   $279.70   $279.70  
  Purchase #2 $143.54   4.242%   $149.629   $149.63   $149.65   $149.60  
  Purchase #3 $65.92   6.853%   $70.4375   $70.44   $70.45   $70.40  
  Purchase #4 $129.35   5.411%   $136.3491   $136.35   $136.35   $136.30  
  Purchase #5 $123.79   3.660%   $128.3207   $128.32   $128.30   $128.30  
  Purchase #6 $159.57   10.615%   $176.5084   $176.51   $176.50   $176.50  
  Purchase #7 $106.25   12.533%   $119.5663   $119.57   $119.55   $119.60  
  7 purchase totals = $975.28       $1,060.4910   $1,060.50   $1,060.50   $1,060.40