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 $204.83   13.160%   $231.7856   $231.79   $231.80   $231.80  
  Purchase #2 $246.99   6.763%   $263.6939   $263.69   $263.70   $263.70  
  Purchase #3 $22.61   9.800%   $24.8258   $24.83   $24.85   $24.80  
  Purchase #4 $58.55   12.155%   $65.6668   $65.67   $65.65   $65.70  
  Purchase #5 $88.79   5.131%   $93.3458   $93.35   $93.35   $93.30  
  Purchase #6 $240.92   4.763%   $252.395   $252.40   $252.40   $252.40  
  Purchase #7 $53.64   12.403%   $60.293   $60.29   $60.30   $60.30  
  7 purchase totals = $916.33       $992.0059   $992.02   $992.05   $992.00