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 $243.71   8.367%   $264.1012   $264.10   $264.10   $264.10  
  Purchase #2 $6.94   12.737%   $7.8239   $7.82   $7.80   $7.80  
  Purchase #3 $109.82   7.546%   $118.107   $118.11   $118.10   $118.10  
  Purchase #4 $23.67   10.603%   $26.1797   $26.18   $26.20   $26.20  
  Purchase #5 $91.93   4.870%   $96.407   $96.41   $96.40   $96.40  
  Purchase #6 $242.45   8.393%   $262.7988   $262.80   $262.80   $262.80  
  Purchase #7 $33.36   7.648%   $35.9114   $35.91   $35.90   $35.90  
  7 purchase totals = $751.88       $811.3290   $811.33   $811.30   $811.30