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 $211.86   7.437%   $227.616   $227.62   $227.60   $227.60  
  Purchase #2 $246.45   8.226%   $266.723   $266.72   $266.70   $266.70  
  Purchase #3 $132.59   11.505%   $147.8445   $147.84   $147.85   $147.80  
  Purchase #4 $68.30   10.357%   $75.3738   $75.37   $75.35   $75.40  
  Purchase #5 $60.26   12.190%   $67.6057   $67.61   $67.60   $67.60  
  Purchase #6 $81.92   10.344%   $90.3938   $90.39   $90.40   $90.40  
  Purchase #7 $53.97   7.305%   $57.9125   $57.91   $57.90   $57.90  
  7 purchase totals = $855.35       $933.4693   $933.46   $933.40   $933.40