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 $229.93   8.578%   $249.6534   $249.65   $249.65   $249.70  
  Purchase #2 $34.47   4.382%   $35.9805   $35.98   $36.00   $36.00  
  Purchase #3 $134.58   12.411%   $151.2827   $151.28   $151.30   $151.30  
  Purchase #4 $156.89   7.843%   $169.1949   $169.19   $169.20   $169.20  
  Purchase #5 $77.69   11.505%   $86.6282   $86.63   $86.65   $86.60  
  Purchase #6 $148.99   11.357%   $165.9108   $165.91   $165.90   $165.90  
  Purchase #7 $204.30   10.631%   $226.0191   $226.02   $226.00   $226.00  
  7 purchase totals = $986.85       $1,084.6696   $1,084.66   $1,084.70   $1,084.70