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 $241.82   4.400%   $252.4601   $252.46   $252.45   $252.50  
  Purchase #2 $237.81   3.786%   $246.8135   $246.81   $246.80   $246.80  
  Purchase #3 $98.40   13.491%   $111.6751   $111.68   $111.70   $111.70  
  Purchase #4 $155.43   5.432%   $163.873   $163.87   $163.85   $163.90  
  Purchase #5 $58.81   5.816%   $62.2304   $62.23   $62.25   $62.20  
  Purchase #6 $99.56   5.810%   $105.3444   $105.34   $105.35   $105.30  
  Purchase #7 $87.82   4.696%   $91.944   $91.94   $91.95   $91.90  
  7 purchase totals = $979.65       $1,034.3405   $1,034.33   $1,034.35   $1,034.30