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 $35.69   4.406%   $37.2625   $37.26   $37.25   $37.30  
  Purchase #2 $241.97   10.320%   $266.9413   $266.94   $266.95   $266.90  
  Purchase #3 $215.44   10.469%   $237.9944   $237.99   $238.00   $238.00  
  Purchase #4 $32.40   11.283%   $36.0557   $36.06   $36.05   $36.10  
  Purchase #5 $12.99   11.862%   $14.5309   $14.53   $14.55   $14.50  
  Purchase #6 $131.59   3.103%   $135.6732   $135.67   $135.65   $135.70  
  Purchase #7 $204.36   11.841%   $228.5583   $228.56   $228.55   $228.60  
  7 purchase totals = $874.44       $957.0163   $957.01   $957.00   $957.10