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 $206.31   9.837%   $226.6047   $226.60   $226.60   $226.60  
  Purchase #2 $230.82   9.263%   $252.2009   $252.20   $252.20   $252.20  
  Purchase #3 $119.55   4.666%   $125.1282   $125.13   $125.15   $125.10  
  Purchase #4 $217.46   5.118%   $228.5896   $228.59   $228.60   $228.60  
  Purchase #5 $6.86   7.824%   $7.3967   $7.40   $7.40   $7.40  
  Purchase #6 $202.62   11.773%   $226.4745   $226.47   $226.45   $226.50  
  Purchase #7 $181.86   10.575%   $201.0917   $201.09   $201.10   $201.10  
  7 purchase totals = $1,165.48       $1,267.4863   $1,267.48   $1,267.50   $1,267.50