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 $219.31   12.198%   $246.0614   $246.06   $246.05   $246.10  
  Purchase #2 $201.44   8.305%   $218.1696   $218.17   $218.15   $218.20  
  Purchase #3 $201.51   11.183%   $224.0449   $224.04   $224.05   $224.00  
  Purchase #4 $26.60   11.304%   $29.6069   $29.61   $29.60   $29.60  
  Purchase #5 $35.43   13.795%   $40.3176   $40.32   $40.30   $40.30  
  Purchase #6 $249.67   3.802%   $259.1625   $259.16   $259.15   $259.20  
  Purchase #7 $61.35   7.247%   $65.796   $65.80   $65.80   $65.80  
  7 purchase totals = $995.31       $1,083.1589   $1,083.16   $1,083.10   $1,083.20