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 $212.25   6.732%   $226.5387   $226.54   $226.55   $226.50  
  Purchase #2 $22.59   6.463%   $24.05   $24.05   $24.05   $24.10  
  Purchase #3 $151.76   7.609%   $163.3074   $163.31   $163.30   $163.30  
  Purchase #4 $8.73   12.271%   $9.8013   $9.80   $9.80   $9.80  
  Purchase #5 $175.94   11.699%   $196.5232   $196.52   $196.50   $196.50  
  Purchase #6 $244.41   10.622%   $270.3712   $270.37   $270.35   $270.40  
  Purchase #7 $50.61   12.198%   $56.7834   $56.78   $56.80   $56.80  
  7 purchase totals = $866.29       $947.3752   $947.37   $947.35   $947.40