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 $62.31   4.328%   $65.0068   $65.01   $65.00   $65.00  
  Purchase #2 $131.76   10.474%   $145.5605   $145.56   $145.55   $145.60  
  Purchase #3 $37.66   10.587%   $41.6471   $41.65   $41.65   $41.60  
  Purchase #4 $217.98   11.194%   $242.3807   $242.38   $242.40   $242.40  
  Purchase #5 $224.34   9.744%   $246.1997   $246.20   $246.20   $246.20  
  Purchase #6 $89.76   12.524%   $101.0015   $101.00   $101.00   $101.00  
  Purchase #7 $122.46   8.342%   $132.6756   $132.68   $132.70   $132.70  
  7 purchase totals = $886.27       $974.4719   $974.48   $974.50   $974.50