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 $30.72   13.842%   $34.9723   $34.97   $34.95   $35.00  
  Purchase #2 $110.59   8.449%   $119.9337   $119.93   $119.95   $119.90  
  Purchase #3 $69.75   5.342%   $73.476   $73.48   $73.50   $73.50  
  Purchase #4 $39.45   6.326%   $41.9456   $41.95   $41.95   $41.90  
  Purchase #5 $158.98   11.322%   $176.9797   $176.98   $177.00   $177.00  
  Purchase #6 $71.83   4.313%   $74.928   $74.93   $74.95   $74.90  
  Purchase #7 $201.32   9.289%   $220.0206   $220.02   $220.00   $220.00  
  7 purchase totals = $682.64       $742.2559   $742.26   $742.30   $742.20