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 $32.89   8.522%   $35.6929   $35.69   $35.70   $35.70  
  Purchase #2 $92.88   5.416%   $97.9104   $97.91   $97.90   $97.90  
  Purchase #3 $75.40   6.337%   $80.1781   $80.18   $80.20   $80.20  
  Purchase #4 $11.81   6.386%   $12.5642   $12.56   $12.55   $12.60  
  Purchase #5 $165.90   5.498%   $175.0212   $175.02   $175.00   $175.00  
  Purchase #6 $170.26   8.673%   $185.0266   $185.03   $185.05   $185.00  
  Purchase #7 $74.69   3.181%   $77.0659   $77.07   $77.05   $77.10  
  7 purchase totals = $623.83       $663.4593   $663.46   $663.45   $663.50