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 $124.39   4.627%   $130.1455   $130.15   $130.15   $130.10  
  Purchase #2 $9.41   3.247%   $9.7155   $9.72   $9.70   $9.70  
  Purchase #3 $39.61   12.866%   $44.7062   $44.71   $44.70   $44.70  
  Purchase #4 $52.74   9.561%   $57.7825   $57.78   $57.80   $57.80  
  Purchase #5 $240.68   6.471%   $256.2544   $256.25   $256.25   $256.30  
  Purchase #6 $165.92   11.315%   $184.6938   $184.69   $184.70   $184.70  
  Purchase #7 $246.30   4.322%   $256.9451   $256.95   $256.95   $256.90  
  7 purchase totals = $879.05       $940.2430   $940.25   $940.25   $940.20