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 $206.67   9.852%   $227.0311   $227.03   $227.05   $227.00  
  Purchase #2 $44.55   11.331%   $49.598   $49.60   $49.60   $49.60  
  Purchase #3 $217.35   4.301%   $226.6982   $226.70   $226.70   $226.70  
  Purchase #4 $15.46   5.573%   $16.3216   $16.32   $16.30   $16.30  
  Purchase #5 $229.32   7.261%   $245.9709   $245.97   $245.95   $246.00  
  Purchase #6 $21.69   13.475%   $24.6127   $24.61   $24.60   $24.60  
  Purchase #7 $188.91   8.625%   $205.2035   $205.20   $205.20   $205.20  
  7 purchase totals = $923.95       $995.4360   $995.43   $995.40   $995.40