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 $177.48   11.822%   $198.4617   $198.46   $198.45   $198.50  
  Purchase #2 $185.86   8.545%   $201.7417   $201.74   $201.75   $201.70  
  Purchase #3 $171.89   12.835%   $193.9521   $193.95   $193.95   $194.00  
  Purchase #4 $33.70   7.343%   $36.1746   $36.17   $36.15   $36.20  
  Purchase #5 $196.96   5.490%   $207.7731   $207.77   $207.75   $207.80  
  Purchase #6 $52.83   9.296%   $57.7411   $57.74   $57.75   $57.70  
  Purchase #7 $100.54   6.191%   $106.7644   $106.76   $106.75   $106.80  
  7 purchase totals = $919.26       $1,002.6087   $1,002.59   $1,002.55   $1,002.70