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 $71.83   6.338%   $76.3826   $76.38   $76.40   $76.40  
  Purchase #2 $113.82   7.862%   $122.7685   $122.77   $122.75   $122.80  
  Purchase #3 $96.88   12.319%   $108.8146   $108.81   $108.80   $108.80  
  Purchase #4 $33.40   12.781%   $37.6689   $37.67   $37.65   $37.70  
  Purchase #5 $28.25   4.679%   $29.5718   $29.57   $29.55   $29.60  
  Purchase #6 $147.48   6.518%   $157.0927   $157.09   $157.10   $157.10  
  Purchase #7 $184.83   4.307%   $192.7906   $192.79   $192.80   $192.80  
  7 purchase totals = $676.49       $725.0897   $725.08   $725.05   $725.20