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 $173.98   10.334%   $191.9591   $191.96   $191.95   $192.00  
  Purchase #2 $249.66   6.767%   $266.5545   $266.55   $266.55   $266.60  
  Purchase #3 $227.49   12.532%   $255.999   $256.00   $256.00   $256.00  
  Purchase #4 $250.37   10.329%   $276.2307   $276.23   $276.25   $276.20  
  Purchase #5 $239.31   9.592%   $262.2646   $262.26   $262.25   $262.30  
  Purchase #6 $241.94   3.580%   $250.6015   $250.60   $250.60   $250.60  
  Purchase #7 $23.93   7.847%   $25.8078   $25.81   $25.80   $25.80  
  7 purchase totals = $1,406.68       $1,529.4172   $1,529.41   $1,529.40   $1,529.50