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 $225.93   12.524%   $254.2255   $254.23   $254.25   $254.20  
  Purchase #2 $212.36   4.163%   $221.2005   $221.20   $221.20   $221.20  
  Purchase #3 $125.45   3.623%   $129.9951   $130.00   $130.00   $130.00  
  Purchase #4 $93.81   3.561%   $97.1506   $97.15   $97.15   $97.20  
  Purchase #5 $177.90   10.578%   $196.7183   $196.72   $196.70   $196.70  
  Purchase #6 $60.34   11.809%   $67.4656   $67.47   $67.45   $67.50  
  Purchase #7 $74.73   8.712%   $81.2405   $81.24   $81.25   $81.20  
  7 purchase totals = $970.52       $1,047.9961   $1,048.01   $1,048.00   $1,048.00