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 $157.70   7.511%   $169.5448   $169.54   $169.55   $169.50  
  Purchase #2 $156.66   11.291%   $174.3485   $174.35   $174.35   $174.30  
  Purchase #3 $125.44   9.397%   $137.2276   $137.23   $137.25   $137.20  
  Purchase #4 $116.67   4.221%   $121.5946   $121.59   $121.60   $121.60  
  Purchase #5 $166.49   5.162%   $175.0842   $175.08   $175.10   $175.10  
  Purchase #6 $127.76   13.830%   $145.4292   $145.43   $145.45   $145.40  
  Purchase #7 $173.67   12.438%   $195.2711   $195.27   $195.25   $195.30  
  7 purchase totals = $1,024.39       $1,118.5000   $1,118.49   $1,118.55   $1,118.40