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 $163.34   13.234%   $184.9564   $184.96   $184.95   $185.00  
  Purchase #2 $168.54   10.595%   $186.3968   $186.40   $186.40   $186.40  
  Purchase #3 $244.96   13.643%   $278.3799   $278.38   $278.40   $278.40  
  Purchase #4 $9.46   8.704%   $10.2834   $10.28   $10.30   $10.30  
  Purchase #5 $191.89   6.385%   $204.1422   $204.14   $204.15   $204.10  
  Purchase #6 $61.72   7.840%   $66.5588   $66.56   $66.55   $66.60  
  Purchase #7 $57.50   11.751%   $64.2568   $64.26   $64.25   $64.30  
  7 purchase totals = $897.41       $994.9743   $994.98   $995.00   $995.10