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 $105.50   12.609%   $118.8025   $118.80   $118.80   $118.80  
  Purchase #2 $56.69   7.116%   $60.7241   $60.72   $60.70   $60.70  
  Purchase #3 $77.66   13.730%   $88.3227   $88.32   $88.30   $88.30  
  Purchase #4 $127.41   8.362%   $138.064   $138.06   $138.05   $138.10  
  Purchase #5 $94.96   6.275%   $100.9187   $100.92   $100.90   $100.90  
  Purchase #6 $214.96   11.651%   $240.005   $240.01   $240.00   $240.00  
  Purchase #7 $25.27   3.833%   $26.2386   $26.24   $26.25   $26.20  
  7 purchase totals = $702.45       $773.0756   $773.07   $773.00   $773.00