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 $149.46   6.217%   $158.7519   $158.75   $158.75   $158.80  
  Purchase #2 $202.40   3.669%   $209.8261   $209.83   $209.85   $209.80  
  Purchase #3 $25.59   10.334%   $28.2345   $28.23   $28.25   $28.20  
  Purchase #4 $86.28   9.238%   $94.2505   $94.25   $94.25   $94.30  
  Purchase #5 $162.96   6.568%   $173.6632   $173.66   $173.65   $173.70  
  Purchase #6 $51.35   10.298%   $56.638   $56.64   $56.65   $56.60  
  Purchase #7 $56.37   9.339%   $61.6344   $61.63   $61.65   $61.60  
  7 purchase totals = $734.41       $782.9986   $782.99   $783.05   $783.00