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 $33.42   6.164%   $35.48   $35.48   $35.50   $35.50  
  Purchase #2 $216.60   9.262%   $236.6615   $236.66   $236.65   $236.70  
  Purchase #3 $129.87   9.446%   $142.1375   $142.14   $142.15   $142.10  
  Purchase #4 $199.44   11.578%   $222.5312   $222.53   $222.55   $222.50  
  Purchase #5 $126.71   7.149%   $135.7685   $135.77   $135.75   $135.80  
  Purchase #6 $66.65   3.486%   $68.9734   $68.97   $68.95   $69.00  
  Purchase #7 $243.89   13.653%   $277.1883   $277.19   $277.20   $277.20  
  7 purchase totals = $1,016.58       $1,118.7404   $1,118.74   $1,118.75   $1,118.80