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 $53.46   12.365%   $60.0703   $60.07   $60.05   $60.10  
  Purchase #2 $242.91   10.734%   $268.984   $268.98   $269.00   $269.00  
  Purchase #3 $170.77   3.580%   $176.8836   $176.88   $176.90   $176.90  
  Purchase #4 $24.87   6.561%   $26.5017   $26.50   $26.50   $26.50  
  Purchase #5 $246.85   11.795%   $275.966   $275.97   $275.95   $276.00  
  Purchase #6 $76.31   10.168%   $84.0692   $84.07   $84.05   $84.10  
  Purchase #7 $163.72   8.532%   $177.6886   $177.69   $177.70   $177.70  
  7 purchase totals = $978.89       $1,070.1634   $1,070.16   $1,070.15   $1,070.30