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 $111.25   13.446%   $126.2087   $126.21   $126.20   $126.20  
  Purchase #2 $183.92   10.233%   $202.7405   $202.74   $202.75   $202.70  
  Purchase #3 $217.93   7.831%   $234.9961   $235.00   $235.00   $235.00  
  Purchase #4 $186.83   9.654%   $204.8666   $204.87   $204.85   $204.90  
  Purchase #5 $217.65   13.610%   $247.2722   $247.27   $247.25   $247.30  
  Purchase #6 $90.74   9.397%   $99.2668   $99.27   $99.25   $99.30  
  Purchase #7 $89.85   12.781%   $101.3337   $101.33   $101.35   $101.30  
  7 purchase totals = $1,098.17       $1,216.6846   $1,216.69   $1,216.65   $1,216.70