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 $163.48   8.198%   $176.8821   $176.88   $176.90   $176.90  
  Purchase #2 $24.60   5.184%   $25.8753   $25.88   $25.90   $25.90  
  Purchase #3 $218.69   11.578%   $244.0099   $244.01   $244.00   $244.00  
  Purchase #4 $237.73   5.377%   $250.5127   $250.51   $250.50   $250.50  
  Purchase #5 $139.53   3.773%   $144.7945   $144.79   $144.80   $144.80  
  Purchase #6 $76.95   11.220%   $85.5838   $85.58   $85.60   $85.60  
  Purchase #7 $89.34   8.853%   $97.2493   $97.25   $97.25   $97.20  
  7 purchase totals = $950.32       $1,024.9076   $1,024.90   $1,024.95   $1,024.90