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 $51.98   8.359%   $56.325   $56.33   $56.35   $56.30  
  Purchase #2 $234.37   8.200%   $253.5883   $253.59   $253.60   $253.60  
  Purchase #3 $10.92   7.791%   $11.7708   $11.77   $11.75   $11.80  
  Purchase #4 $249.97   8.673%   $271.6499   $271.65   $271.65   $271.60  
  Purchase #5 $143.78   6.144%   $152.6138   $152.61   $152.60   $152.60  
  Purchase #6 $61.94   5.585%   $65.3993   $65.40   $65.40   $65.40  
  Purchase #7 $97.56   9.252%   $106.5863   $106.59   $106.60   $106.60  
  7 purchase totals = $850.52       $917.9334   $917.94   $917.95   $917.90