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 $246.62   10.578%   $272.7075   $272.71   $272.70   $272.70  
  Purchase #2 $86.98   9.436%   $95.1874   $95.19   $95.20   $95.20  
  Purchase #3 $89.70   8.690%   $97.4949   $97.49   $97.50   $97.50  
  Purchase #4 $212.42   4.607%   $222.2062   $222.21   $222.20   $222.20  
  Purchase #5 $173.81   7.513%   $186.8683   $186.87   $186.85   $186.90  
  Purchase #6 $246.49   12.670%   $277.7203   $277.72   $277.70   $277.70  
  Purchase #7 $62.55   12.597%   $70.4294   $70.43   $70.45   $70.40  
  7 purchase totals = $1,118.57       $1,222.6140   $1,222.62   $1,222.60   $1,222.60