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 $242.54   8.654%   $263.5294   $263.53   $263.55   $263.50  
  Purchase #2 $194.32   6.329%   $206.6185   $206.62   $206.60   $206.60  
  Purchase #3 $241.88   11.517%   $269.7373   $269.74   $269.75   $269.70  
  Purchase #4 $75.88   13.553%   $86.164   $86.16   $86.15   $86.20  
  Purchase #5 $148.75   5.427%   $156.8227   $156.82   $156.80   $156.80  
  Purchase #6 $169.85   3.320%   $175.489   $175.49   $175.50   $175.50  
  Purchase #7 $46.87   7.629%   $50.4457   $50.45   $50.45   $50.40  
  7 purchase totals = $1,120.09       $1,208.8066   $1,208.81   $1,208.80   $1,208.70