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 $41.66   11.655%   $46.5155   $46.52   $46.50   $46.50  
  Purchase #2 $184.52   9.205%   $201.5051   $201.51   $201.50   $201.50  
  Purchase #3 $63.37   12.840%   $71.5067   $71.51   $71.50   $71.50  
  Purchase #4 $189.90   12.832%   $214.268   $214.27   $214.25   $214.30  
  Purchase #5 $71.67   3.861%   $74.4372   $74.44   $74.45   $74.40  
  Purchase #6 $233.69   7.113%   $250.3124   $250.31   $250.30   $250.30  
  Purchase #7 $207.61   13.867%   $236.3993   $236.40   $236.40   $236.40  
  7 purchase totals = $992.42       $1,094.9442   $1,094.96   $1,094.90   $1,094.90