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 $97.68   9.221%   $106.6871   $106.69   $106.70   $106.70  
  Purchase #2 $180.76   13.757%   $205.6272   $205.63   $205.65   $205.60  
  Purchase #3 $77.81   9.863%   $85.4844   $85.48   $85.50   $85.50  
  Purchase #4 $52.52   7.853%   $56.6444   $56.64   $56.65   $56.60  
  Purchase #5 $166.41   11.395%   $185.3724   $185.37   $185.35   $185.40  
  Purchase #6 $143.61   6.378%   $152.7694   $152.77   $152.75   $152.80  
  Purchase #7 $239.49   12.578%   $269.6131   $269.61   $269.60   $269.60  
  7 purchase totals = $958.28       $1,062.1980   $1,062.19   $1,062.20   $1,062.20