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 $146.99   8.246%   $159.1108   $159.11   $159.10   $159.10  
  Purchase #2 $197.55   4.138%   $205.7246   $205.72   $205.70   $205.70  
  Purchase #3 $106.99   11.477%   $119.2692   $119.27   $119.25   $119.30  
  Purchase #4 $89.55   9.366%   $97.9373   $97.94   $97.95   $97.90  
  Purchase #5 $149.80   10.411%   $165.3957   $165.40   $165.40   $165.40  
  Purchase #6 $150.30   12.292%   $168.7749   $168.77   $168.75   $168.80  
  Purchase #7 $32.85   3.576%   $34.0247   $34.02   $34.00   $34.00  
  7 purchase totals = $874.03       $950.2372   $950.23   $950.15   $950.20