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 $246.62   11.788%   $275.6916   $275.69   $275.70   $275.70  
  Purchase #2 $154.71   9.868%   $169.9768   $169.98   $170.00   $170.00  
  Purchase #3 $180.28   12.495%   $202.806   $202.81   $202.80   $202.80  
  Purchase #4 $161.83   3.563%   $167.596   $167.60   $167.60   $167.60  
  Purchase #5 $11.92   5.489%   $12.5743   $12.57   $12.55   $12.60  
  Purchase #6 $196.44   8.675%   $213.4812   $213.48   $213.50   $213.50  
  Purchase #7 $103.26   10.259%   $113.8534   $113.85   $113.85   $113.90  
  7 purchase totals = $1,055.06       $1,155.9793   $1,155.98   $1,156.00   $1,156.10