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 $88.89   8.771%   $96.6865   $96.69   $96.70   $96.70  
  Purchase #2 $245.69   13.153%   $278.0056   $278.01   $278.00   $278.00  
  Purchase #3 $192.47   7.304%   $206.528   $206.53   $206.55   $206.50  
  Purchase #4 $147.29   12.812%   $166.1608   $166.16   $166.15   $166.20  
  Purchase #5 $231.90   9.150%   $253.1189   $253.12   $253.10   $253.10  
  Purchase #6 $237.45   3.265%   $245.2027   $245.20   $245.20   $245.20  
  Purchase #7 $47.69   6.328%   $50.7078   $50.71   $50.70   $50.70  
  7 purchase totals = $1,191.38       $1,296.4103   $1,296.42   $1,296.40   $1,296.40