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 $153.81   13.692%   $174.8697   $174.87   $174.85   $174.90  
  Purchase #2 $177.50   11.443%   $197.8113   $197.81   $197.80   $197.80  
  Purchase #3 $10.50   6.855%   $11.2198   $11.22   $11.20   $11.20  
  Purchase #4 $244.45   13.665%   $277.8541   $277.85   $277.85   $277.90  
  Purchase #5 $115.78   8.494%   $125.6144   $125.61   $125.60   $125.60  
  Purchase #6 $25.63   6.522%   $27.3016   $27.30   $27.30   $27.30  
  Purchase #7 $68.65   10.699%   $75.9949   $75.99   $76.00   $76.00  
  7 purchase totals = $796.32       $890.6658   $890.65   $890.60   $890.70