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 $193.79   6.435%   $206.2604   $206.26   $206.25   $206.30  
  Purchase #2 $181.75   6.395%   $193.3729   $193.37   $193.35   $193.40  
  Purchase #3 $243.61   9.663%   $267.15   $267.15   $267.15   $267.20  
  Purchase #4 $228.91   6.826%   $244.5354   $244.54   $244.55   $244.50  
  Purchase #5 $155.40   7.421%   $166.9322   $166.93   $166.95   $166.90  
  Purchase #6 $202.77   6.210%   $215.362   $215.36   $215.35   $215.40  
  Purchase #7 $200.69   12.731%   $226.2398   $226.24   $226.25   $226.20  
  7 purchase totals = $1,406.92       $1,519.8527   $1,519.85   $1,519.85   $1,519.90