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 $196.75   13.778%   $223.8582   $223.86   $223.85   $223.90  
  Purchase #2 $68.35   11.377%   $76.1262   $76.13   $76.15   $76.10  
  Purchase #3 $213.29   8.445%   $231.3023   $231.30   $231.30   $231.30  
  Purchase #4 $34.82   12.828%   $39.2867   $39.29   $39.30   $39.30  
  Purchase #5 $162.53   6.685%   $173.3951   $173.40   $173.40   $173.40  
  Purchase #6 $231.66   3.513%   $239.7982   $239.80   $239.80   $239.80  
  Purchase #7 $63.89   4.348%   $66.6679   $66.67   $66.65   $66.70  
  7 purchase totals = $971.29       $1,050.4346   $1,050.45   $1,050.45   $1,050.50