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 $168.90   13.580%   $191.8366   $191.84   $191.85   $191.80  
  Purchase #2 $58.38   6.704%   $62.2938   $62.29   $62.30   $62.30  
  Purchase #3 $33.30   7.531%   $35.8078   $35.81   $35.80   $35.80  
  Purchase #4 $193.91   9.574%   $212.4749   $212.47   $212.45   $212.50  
  Purchase #5 $220.55   9.280%   $241.017   $241.02   $241.00   $241.00  
  Purchase #6 $78.99   5.571%   $83.3905   $83.39   $83.40   $83.40  
  Purchase #7 $165.93   4.488%   $173.3769   $173.38   $173.40   $173.40  
  7 purchase totals = $919.96       $1,000.1975   $1,000.20   $1,000.20   $1,000.20