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 $69.54   11.633%   $77.6296   $77.63   $77.65   $77.60  
  Purchase #2 $63.99   12.812%   $72.1884   $72.19   $72.20   $72.20  
  Purchase #3 $29.89   10.687%   $33.0843   $33.08   $33.10   $33.10  
  Purchase #4 $118.44   12.413%   $133.142   $133.14   $133.15   $133.10  
  Purchase #5 $137.99   5.340%   $145.3587   $145.36   $145.35   $145.40  
  Purchase #6 $118.79   6.823%   $126.895   $126.90   $126.90   $126.90  
  Purchase #7 $6.32   11.687%   $7.0586   $7.06   $7.05   $7.10  
  7 purchase totals = $544.96       $595.3566   $595.36   $595.40   $595.40