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 $61.72   11.173%   $68.616   $68.62   $68.60   $68.60  
  Purchase #2 $127.63   8.645%   $138.6636   $138.66   $138.65   $138.70  
  Purchase #3 $163.81   9.857%   $179.9568   $179.96   $179.95   $180.00  
  Purchase #4 $231.25   13.857%   $263.2943   $263.29   $263.30   $263.30  
  Purchase #5 $56.79   6.137%   $60.2752   $60.28   $60.30   $60.30  
  Purchase #6 $202.69   12.247%   $227.5134   $227.51   $227.50   $227.50  
  Purchase #7 $119.96   11.675%   $133.9653   $133.97   $133.95   $134.00  
  7 purchase totals = $963.85       $1,072.2846   $1,072.29   $1,072.25   $1,072.40