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 $171.32   8.115%   $185.2226   $185.22   $185.20   $185.20  
  Purchase #2 $30.91   8.689%   $33.5958   $33.60   $33.60   $33.60  
  Purchase #3 $112.96   4.640%   $118.2013   $118.20   $118.20   $118.20  
  Purchase #4 $249.68   12.387%   $280.6079   $280.61   $280.60   $280.60  
  Purchase #5 $248.43   4.464%   $259.5199   $259.52   $259.50   $259.50  
  Purchase #6 $232.64   8.560%   $252.554   $252.55   $252.55   $252.60  
  Purchase #7 $58.28   11.537%   $65.0038   $65.00   $65.00   $65.00  
  7 purchase totals = $1,104.22       $1,194.7053   $1,194.70   $1,194.65   $1,194.70