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 $142.71   6.456%   $151.9234   $151.92   $151.90   $151.90  
  Purchase #2 $244.76   11.418%   $272.7067   $272.71   $272.70   $272.70  
  Purchase #3 $111.56   12.658%   $125.6813   $125.68   $125.70   $125.70  
  Purchase #4 $179.72   12.544%   $202.2641   $202.26   $202.25   $202.30  
  Purchase #5 $5.97   8.275%   $6.464   $6.46   $6.45   $6.50  
  Purchase #6 $151.54   6.871%   $161.9523   $161.95   $161.95   $162.00  
  Purchase #7 $163.25   6.493%   $173.8498   $173.85   $173.85   $173.80  
  7 purchase totals = $999.51       $1,094.8416   $1,094.83   $1,094.80   $1,094.90