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 $34.77   5.311%   $36.6166   $36.62   $36.60   $36.60  
  Purchase #2 $99.86   12.709%   $112.5512   $112.55   $112.55   $112.60  
  Purchase #3 $85.30   13.821%   $97.0893   $97.09   $97.10   $97.10  
  Purchase #4 $174.29   9.594%   $191.0114   $191.01   $191.00   $191.00  
  Purchase #5 $70.64   13.865%   $80.4342   $80.43   $80.45   $80.40  
  Purchase #6 $196.36   9.622%   $215.2538   $215.25   $215.25   $215.30  
  Purchase #7 $41.42   5.216%   $43.5805   $43.58   $43.60   $43.60  
  7 purchase totals = $702.64       $776.5370   $776.53   $776.55   $776.60