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 $209.62   6.124%   $222.4571   $222.46   $222.45   $222.50  
  Purchase #2 $58.79   8.813%   $63.9712   $63.97   $63.95   $64.00  
  Purchase #3 $62.86   9.377%   $68.7544   $68.75   $68.75   $68.80  
  Purchase #4 $245.56   9.524%   $268.9471   $268.95   $268.95   $268.90  
  Purchase #5 $177.56   13.206%   $201.0086   $201.01   $201.00   $201.00  
  Purchase #6 $207.68   3.318%   $214.5708   $214.57   $214.55   $214.60  
  Purchase #7 $78.25   8.307%   $84.7502   $84.75   $84.75   $84.80  
  7 purchase totals = $1,040.32       $1,124.4594   $1,124.46   $1,124.40   $1,124.60