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 $118.51   3.518%   $122.6792   $122.68   $122.70   $122.70  
  Purchase #2 $151.88   9.330%   $166.0504   $166.05   $166.05   $166.10  
  Purchase #3 $34.33   7.501%   $36.9051   $36.91   $36.90   $36.90  
  Purchase #4 $183.35   11.403%   $204.2574   $204.26   $204.25   $204.30  
  Purchase #5 $23.86   9.533%   $26.1346   $26.13   $26.15   $26.10  
  Purchase #6 $205.66   11.254%   $228.805   $228.81   $228.80   $228.80  
  Purchase #7 $177.95   11.138%   $197.7701   $197.77   $197.75   $197.80  
  7 purchase totals = $895.54       $982.6018   $982.61   $982.60   $982.70