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 $210.44   10.617%   $232.7824   $232.78   $232.80   $232.80  
  Purchase #2 $89.95   6.218%   $95.5431   $95.54   $95.55   $95.50  
  Purchase #3 $159.61   5.286%   $168.047   $168.05   $168.05   $168.00  
  Purchase #4 $103.45   7.636%   $111.3494   $111.35   $111.35   $111.30  
  Purchase #5 $234.66   9.449%   $256.833   $256.83   $256.85   $256.80  
  Purchase #6 $73.95   12.535%   $83.2196   $83.22   $83.20   $83.20  
  Purchase #7 $163.37   7.122%   $175.0052   $175.01   $175.00   $175.00  
  7 purchase totals = $1,035.43       $1,122.7797   $1,122.78   $1,122.80   $1,122.60