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 $33.69   11.776%   $37.6573   $37.66   $37.65   $37.70  
  Purchase #2 $115.97   13.529%   $131.6596   $131.66   $131.65   $131.70  
  Purchase #3 $94.91   13.421%   $107.6479   $107.65   $107.65   $107.60  
  Purchase #4 $156.31   5.724%   $165.2572   $165.26   $165.25   $165.30  
  Purchase #5 $204.92   12.813%   $231.1764   $231.18   $231.20   $231.20  
  Purchase #6 $198.43   5.181%   $208.7107   $208.71   $208.70   $208.70  
  Purchase #7 $126.35   3.548%   $130.8329   $130.83   $130.85   $130.80  
  7 purchase totals = $930.58       $1,012.9420   $1,012.95   $1,012.95   $1,013.00