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 $51.53   5.481%   $54.3544   $54.35   $54.35   $54.40  
  Purchase #2 $109.32   12.150%   $122.6024   $122.60   $122.60   $122.60  
  Purchase #3 $176.68   13.658%   $200.811   $200.81   $200.80   $200.80  
  Purchase #4 $98.49   5.271%   $103.6814   $103.68   $103.70   $103.70  
  Purchase #5 $133.93   11.142%   $148.8525   $148.85   $148.85   $148.90  
  Purchase #6 $161.72   8.237%   $175.0409   $175.04   $175.05   $175.00  
  Purchase #7 $53.85   4.239%   $56.1327   $56.13   $56.15   $56.10  
  7 purchase totals = $785.52       $861.4753   $861.46   $861.50   $861.50