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 $145.47   11.839%   $162.6922   $162.69   $162.70   $162.70  
  Purchase #2 $174.95   13.149%   $197.9542   $197.95   $197.95   $198.00  
  Purchase #3 $79.38   11.746%   $88.704   $88.70   $88.70   $88.70  
  Purchase #4 $118.95   7.188%   $127.5001   $127.50   $127.50   $127.50  
  Purchase #5 $50.39   10.826%   $55.8452   $55.85   $55.85   $55.80  
  Purchase #6 $151.65   12.501%   $170.6078   $170.61   $170.60   $170.60  
  Purchase #7 $115.41   4.388%   $120.4742   $120.47   $120.45   $120.50  
  7 purchase totals = $836.20       $923.7777   $923.77   $923.75   $923.80