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 $95.28   11.209%   $105.9599   $105.96   $105.95   $106.00  
  Purchase #2 $11.62   13.536%   $13.1929   $13.19   $13.20   $13.20  
  Purchase #3 $93.77   6.493%   $99.8585   $99.86   $99.85   $99.90  
  Purchase #4 $60.38   8.758%   $65.6681   $65.67   $65.65   $65.70  
  Purchase #5 $187.38   9.833%   $205.8051   $205.81   $205.80   $205.80  
  Purchase #6 $161.77   6.582%   $172.4177   $172.42   $172.40   $172.40  
  Purchase #7 $216.53   6.854%   $231.371   $231.37   $231.35   $231.40  
  7 purchase totals = $826.73       $894.2732   $894.28   $894.20   $894.40