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 $30.69   6.193%   $32.5906   $32.59   $32.60   $32.60  
  Purchase #2 $213.76   4.826%   $224.0761   $224.08   $224.10   $224.10  
  Purchase #3 $210.26   5.462%   $221.7444   $221.74   $221.75   $221.70  
  Purchase #4 $156.25   4.457%   $163.2141   $163.21   $163.20   $163.20  
  Purchase #5 $70.49   7.656%   $75.8867   $75.89   $75.90   $75.90  
  Purchase #6 $86.59   11.327%   $96.398   $96.40   $96.40   $96.40  
  Purchase #7 $210.26   6.457%   $223.8365   $223.84   $223.85   $223.80  
  7 purchase totals = $978.30       $1,037.7464   $1,037.75   $1,037.80   $1,037.70