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 $164.35   6.159%   $174.4723   $174.47   $174.45   $174.50  
  Purchase #2 $239.59   11.872%   $268.0341   $268.03   $268.05   $268.00  
  Purchase #3 $187.43   4.519%   $195.9   $195.90   $195.90   $195.90  
  Purchase #4 $25.89   5.132%   $27.2187   $27.22   $27.20   $27.20  
  Purchase #5 $159.92   8.759%   $173.9274   $173.93   $173.95   $173.90  
  Purchase #6 $239.52   13.309%   $271.3977   $271.40   $271.40   $271.40  
  Purchase #7 $85.30   5.824%   $90.2679   $90.27   $90.25   $90.30  
  7 purchase totals = $1,102.00       $1,201.2181   $1,201.22   $1,201.20   $1,201.20