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 $60.50   3.716%   $62.7482   $62.75   $62.75   $62.70  
  Purchase #2 $171.69   5.654%   $181.3974   $181.40   $181.40   $181.40  
  Purchase #3 $122.57   13.341%   $138.9221   $138.92   $138.90   $138.90  
  Purchase #4 $85.61   13.666%   $97.3095   $97.31   $97.30   $97.30  
  Purchase #5 $51.60   6.138%   $54.7672   $54.77   $54.75   $54.80  
  Purchase #6 $240.99   5.268%   $253.6854   $253.69   $253.70   $253.70  
  Purchase #7 $49.69   9.513%   $54.417   $54.42   $54.40   $54.40  
  7 purchase totals = $782.65       $843.2468   $843.26   $843.20   $843.20