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 $62.49   13.713%   $71.0593   $71.06   $71.05   $71.10  
  Purchase #2 $27.97   9.341%   $30.5827   $30.58   $30.60   $30.60  
  Purchase #3 $183.43   7.178%   $196.5966   $196.60   $196.60   $196.60  
  Purchase #4 $115.74   13.151%   $130.961   $130.96   $130.95   $131.00  
  Purchase #5 $25.35   13.157%   $28.6853   $28.69   $28.70   $28.70  
  Purchase #6 $92.54   5.674%   $97.7907   $97.79   $97.80   $97.80  
  Purchase #7 $234.77   7.654%   $252.7393   $252.74   $252.75   $252.70  
  7 purchase totals = $742.29       $808.4149   $808.42   $808.45   $808.50