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 $236.95   13.113%   $268.0213   $268.02   $268.00   $268.00  
  Purchase #2 $47.80   7.267%   $51.2736   $51.27   $51.25   $51.30  
  Purchase #3 $189.31   7.646%   $203.7846   $203.78   $203.80   $203.80  
  Purchase #4 $154.28   7.355%   $165.6273   $165.63   $165.65   $165.60  
  Purchase #5 $207.29   13.184%   $234.6191   $234.62   $234.60   $234.60  
  Purchase #6 $55.27   3.112%   $56.99   $56.99   $57.00   $57.00  
  Purchase #7 $114.42   6.820%   $122.2234   $122.22   $122.20   $122.20  
  7 purchase totals = $1,005.32       $1,102.5393   $1,102.53   $1,102.50   $1,102.50