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 $205.70   3.400%   $212.6938   $212.69   $212.70   $212.70  
  Purchase #2 $60.27   8.219%   $65.2236   $65.22   $65.20   $65.20  
  Purchase #3 $153.90   13.462%   $174.618   $174.62   $174.60   $174.60  
  Purchase #4 $162.68   7.435%   $174.7753   $174.78   $174.80   $174.80  
  Purchase #5 $91.99   3.864%   $95.5445   $95.54   $95.55   $95.50  
  Purchase #6 $151.98   8.105%   $164.298   $164.30   $164.30   $164.30  
  Purchase #7 $104.64   8.417%   $113.4475   $113.45   $113.45   $113.40  
  7 purchase totals = $931.16       $1,000.6007   $1,000.60   $1,000.60   $1,000.50