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 $52.47   9.835%   $57.6304   $57.63   $57.65   $57.60  
  Purchase #2 $79.67   12.723%   $89.8064   $89.81   $89.80   $89.80  
  Purchase #3 $156.26   6.703%   $166.7341   $166.73   $166.75   $166.70  
  Purchase #4 $211.40   4.171%   $220.2175   $220.22   $220.20   $220.20  
  Purchase #5 $96.55   10.289%   $106.484   $106.48   $106.50   $106.50  
  Purchase #6 $154.52   12.395%   $173.6728   $173.67   $173.65   $173.70  
  Purchase #7 $98.75   11.224%   $109.8337   $109.83   $109.85   $109.80  
  7 purchase totals = $849.62       $924.3789   $924.37   $924.40   $924.30