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 $65.66   6.543%   $69.9561   $69.96   $69.95   $70.00  
  Purchase #2 $147.73   4.292%   $154.0706   $154.07   $154.05   $154.10  
  Purchase #3 $11.58   9.762%   $12.7104   $12.71   $12.70   $12.70  
  Purchase #4 $111.45   9.247%   $121.7558   $121.76   $121.75   $121.80  
  Purchase #5 $236.56   4.343%   $246.8338   $246.83   $246.85   $246.80  
  Purchase #6 $97.40   6.310%   $103.5459   $103.55   $103.55   $103.50  
  Purchase #7 $226.50   10.865%   $251.1092   $251.11   $251.10   $251.10  
  7 purchase totals = $896.88       $959.9818   $959.99   $959.95   $960.00