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 $45.43   4.785%   $47.6038   $47.60   $47.60   $47.60  
  Purchase #2 $97.82   12.379%   $109.9291   $109.93   $109.95   $109.90  
  Purchase #3 $206.79   13.162%   $234.0077   $234.01   $234.00   $234.00  
  Purchase #4 $228.77   9.838%   $251.2764   $251.28   $251.30   $251.30  
  Purchase #5 $198.38   7.390%   $213.0403   $213.04   $213.05   $213.00  
  Purchase #6 $13.55   6.576%   $14.441   $14.44   $14.45   $14.40  
  Purchase #7 $206.75   9.297%   $225.9715   $225.97   $225.95   $226.00  
  7 purchase totals = $997.49       $1,096.2698   $1,096.27   $1,096.30   $1,096.20