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 $169.37   6.711%   $180.7364   $180.74   $180.75   $180.70  
  Purchase #2 $176.39   8.431%   $191.2614   $191.26   $191.25   $191.30  
  Purchase #3 $109.85   8.173%   $118.828   $118.83   $118.85   $118.80  
  Purchase #4 $40.83   6.366%   $43.4292   $43.43   $43.45   $43.40  
  Purchase #5 $168.81   4.834%   $176.9703   $176.97   $176.95   $177.00  
  Purchase #6 $90.49   6.498%   $96.37   $96.37   $96.35   $96.40  
  Purchase #7 $238.73   11.394%   $265.9309   $265.93   $265.95   $265.90  
  7 purchase totals = $994.47       $1,073.5262   $1,073.53   $1,073.55   $1,073.50