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 $77.33   11.611%   $86.3088   $86.31   $86.30   $86.30  
  Purchase #2 $234.99   5.396%   $247.6701   $247.67   $247.65   $247.70  
  Purchase #3 $207.87   4.256%   $216.7169   $216.72   $216.70   $216.70  
  Purchase #4 $174.83   11.400%   $194.7606   $194.76   $194.75   $194.80  
  Purchase #5 $157.80   6.820%   $168.562   $168.56   $168.55   $168.60  
  Purchase #6 $124.49   11.640%   $138.9806   $138.98   $139.00   $139.00  
  Purchase #7 $246.30   9.233%   $269.0409   $269.04   $269.05   $269.00  
  7 purchase totals = $1,223.61       $1,322.0399   $1,322.04   $1,322.00   $1,322.10