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 $65.87   8.296%   $71.3346   $71.33   $71.35   $71.30  
  Purchase #2 $69.53   12.121%   $77.9577   $77.96   $77.95   $78.00  
  Purchase #3 $219.26   3.201%   $226.2785   $226.28   $226.30   $226.30  
  Purchase #4 $76.36   13.684%   $86.8091   $86.81   $86.80   $86.80  
  Purchase #5 $71.83   12.557%   $80.8497   $80.85   $80.85   $80.80  
  Purchase #6 $112.29   11.125%   $124.7823   $124.78   $124.80   $124.80  
  Purchase #7 $25.28   6.737%   $26.9831   $26.98   $27.00   $27.00  
  7 purchase totals = $640.42       $694.9950   $694.99   $695.05   $695.00