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 $238.35   12.400%   $267.9054   $267.91   $267.90   $267.90  
  Purchase #2 $165.46   9.149%   $180.5979   $180.60   $180.60   $180.60  
  Purchase #3 $204.54   8.324%   $221.5659   $221.57   $221.55   $221.60  
  Purchase #4 $43.37   10.246%   $47.8137   $47.81   $47.80   $47.80  
  Purchase #5 $210.30   8.779%   $228.7622   $228.76   $228.75   $228.80  
  Purchase #6 $16.87   5.338%   $17.7705   $17.77   $17.75   $17.80  
  Purchase #7 $162.46   8.725%   $176.6346   $176.63   $176.65   $176.60  
  7 purchase totals = $1,041.35       $1,141.0502   $1,141.05   $1,141.00   $1,141.10