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 $66.62   4.102%   $69.3528   $69.35   $69.35   $69.40  
  Purchase #2 $146.56   6.404%   $155.9457   $155.95   $155.95   $155.90  
  Purchase #3 $238.77   4.434%   $249.3571   $249.36   $249.35   $249.40  
  Purchase #4 $95.30   12.162%   $106.8904   $106.89   $106.90   $106.90  
  Purchase #5 $186.28   11.566%   $207.8251   $207.83   $207.85   $207.80  
  Purchase #6 $5.65   8.706%   $6.1419   $6.14   $6.15   $6.10  
  Purchase #7 $239.40   6.182%   $254.1997   $254.20   $254.20   $254.20  
  7 purchase totals = $978.58       $1,049.7127   $1,049.72   $1,049.75   $1,049.70