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 $200.55   9.575%   $219.7527   $219.75   $219.75   $219.80  
  Purchase #2 $100.65   6.240%   $106.9306   $106.93   $106.95   $106.90  
  Purchase #3 $68.89   9.777%   $75.6254   $75.63   $75.65   $75.60  
  Purchase #4 $166.30   5.524%   $175.4864   $175.49   $175.50   $175.50  
  Purchase #5 $247.72   7.458%   $266.195   $266.20   $266.20   $266.20  
  Purchase #6 $96.69   6.785%   $103.2504   $103.25   $103.25   $103.30  
  Purchase #7 $81.89   4.710%   $85.747   $85.75   $85.75   $85.70  
  7 purchase totals = $962.69       $1,032.9875   $1,033.00   $1,033.05   $1,033.00