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 $240.44   10.194%   $264.9505   $264.95   $264.95   $265.00  
  Purchase #2 $96.87   8.745%   $105.3413   $105.34   $105.35   $105.30  
  Purchase #3 $79.59   10.317%   $87.8013   $87.80   $87.80   $87.80  
  Purchase #4 $211.98   6.141%   $224.9977   $225.00   $225.00   $225.00  
  Purchase #5 $190.66   7.866%   $205.6573   $205.66   $205.65   $205.70  
  Purchase #6 $149.40   10.619%   $165.2648   $165.26   $165.25   $165.30  
  Purchase #7 $127.61   5.466%   $134.5852   $134.59   $134.60   $134.60  
  7 purchase totals = $1,096.55       $1,188.5981   $1,188.60   $1,188.60   $1,188.70