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 $50.78   4.373%   $53.0006   $53.00   $53.00   $53.00  
  Purchase #2 $246.34   3.375%   $254.654   $254.65   $254.65   $254.70  
  Purchase #3 $65.76   3.477%   $68.0465   $68.05   $68.05   $68.00  
  Purchase #4 $86.60   4.537%   $90.529   $90.53   $90.55   $90.50  
  Purchase #5 $19.87   3.395%   $20.5446   $20.54   $20.55   $20.50  
  Purchase #6 $222.90   3.353%   $230.3738   $230.37   $230.35   $230.40  
  Purchase #7 $221.25   4.486%   $231.1753   $231.18   $231.20   $231.20  
  7 purchase totals = $913.50       $948.3238   $948.32   $948.35   $948.30