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 $61.39   10.828%   $68.0373   $68.04   $68.05   $68.00  
  Purchase #2 $49.66   13.349%   $56.2891   $56.29   $56.30   $56.30  
  Purchase #3 $116.68   12.257%   $130.9815   $130.98   $131.00   $131.00  
  Purchase #4 $214.51   6.469%   $228.3867   $228.39   $228.40   $228.40  
  Purchase #5 $32.54   8.369%   $35.2633   $35.26   $35.25   $35.30  
  Purchase #6 $124.77   11.821%   $139.5191   $139.52   $139.50   $139.50  
  Purchase #7 $155.42   6.848%   $166.0632   $166.06   $166.05   $166.10  
  7 purchase totals = $754.97       $824.5402   $824.54   $824.55   $824.60