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 $234.52   5.127%   $246.5438   $246.54   $246.55   $246.50  
  Purchase #2 $16.30   12.623%   $18.3575   $18.36   $18.35   $18.40  
  Purchase #3 $181.75   12.535%   $204.5324   $204.53   $204.55   $204.50  
  Purchase #4 $190.53   12.670%   $214.6702   $214.67   $214.65   $214.70  
  Purchase #5 $86.26   4.197%   $89.8803   $89.88   $89.90   $89.90  
  Purchase #6 $100.98   11.834%   $112.93   $112.93   $112.95   $112.90  
  Purchase #7 $175.83   6.190%   $186.7139   $186.71   $186.70   $186.70  
  7 purchase totals = $986.17       $1,073.6281   $1,073.62   $1,073.65   $1,073.60