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 $52.76   11.795%   $58.983   $58.98   $59.00   $59.00  
  Purchase #2 $209.86   10.354%   $231.5889   $231.59   $231.60   $231.60  
  Purchase #3 $212.55   3.291%   $219.545   $219.55   $219.55   $219.50  
  Purchase #4 $236.98   7.645%   $255.0971   $255.10   $255.10   $255.10  
  Purchase #5 $5.69   12.662%   $6.4105   $6.41   $6.40   $6.40  
  Purchase #6 $74.50   7.570%   $80.1397   $80.14   $80.15   $80.10  
  Purchase #7 $90.94   7.490%   $97.7514   $97.75   $97.75   $97.80  
  7 purchase totals = $883.28       $949.5156   $949.52   $949.55   $949.50