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 $92.77   5.181%   $97.5764   $97.58   $97.60   $97.60  
  Purchase #2 $179.33   12.246%   $201.2908   $201.29   $201.30   $201.30  
  Purchase #3 $55.32   8.346%   $59.937   $59.94   $59.95   $59.90  
  Purchase #4 $85.45   11.160%   $94.9862   $94.99   $95.00   $95.00  
  Purchase #5 $138.94   9.279%   $151.8322   $151.83   $151.85   $151.80  
  Purchase #6 $183.63   6.548%   $195.6541   $195.65   $195.65   $195.70  
  Purchase #7 $50.25   6.865%   $53.6997   $53.70   $53.70   $53.70  
  7 purchase totals = $785.69       $854.9764   $854.98   $855.05   $855.00