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 $49.43   5.810%   $52.3019   $52.30   $52.30   $52.30  
  Purchase #2 $224.91   11.416%   $250.5857   $250.59   $250.60   $250.60  
  Purchase #3 $26.61   6.177%   $28.2537   $28.25   $28.25   $28.30  
  Purchase #4 $109.47   5.442%   $115.4274   $115.43   $115.45   $115.40  
  Purchase #5 $211.77   9.609%   $232.119   $232.12   $232.10   $232.10  
  Purchase #6 $110.41   6.827%   $117.9477   $117.95   $117.95   $117.90  
  Purchase #7 $116.87   12.862%   $131.9018   $131.90   $131.90   $131.90  
  7 purchase totals = $849.47       $928.5372   $928.54   $928.55   $928.50