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 $240.25   12.354%   $269.9305   $269.93   $269.95   $269.90  
  Purchase #2 $26.57   5.682%   $28.0797   $28.08   $28.10   $28.10  
  Purchase #3 $86.99   8.656%   $94.5199   $94.52   $94.50   $94.50  
  Purchase #4 $133.29   8.454%   $144.5583   $144.56   $144.55   $144.60  
  Purchase #5 $123.91   5.445%   $130.6569   $130.66   $130.65   $130.70  
  Purchase #6 $80.69   6.111%   $85.621   $85.62   $85.60   $85.60  
  Purchase #7 $115.84   11.774%   $129.479   $129.48   $129.50   $129.50  
  7 purchase totals = $807.54       $882.8453   $882.85   $882.85   $882.90