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 $168.75   6.110%   $179.0606   $179.06   $179.05   $179.10  
  Purchase #2 $104.57   11.295%   $116.3812   $116.38   $116.40   $116.40  
  Purchase #3 $92.89   10.484%   $102.6286   $102.63   $102.65   $102.60  
  Purchase #4 $230.80   3.676%   $239.2842   $239.28   $239.30   $239.30  
  Purchase #5 $109.33   8.418%   $118.5334   $118.53   $118.55   $118.50  
  Purchase #6 $167.40   3.121%   $172.6246   $172.62   $172.60   $172.60  
  Purchase #7 $19.40   12.191%   $21.7651   $21.77   $21.75   $21.80  
  7 purchase totals = $893.14       $950.2777   $950.27   $950.30   $950.30