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 $87.62   10.248%   $96.5993   $96.60   $96.60   $96.60  
  Purchase #2 $24.73   7.124%   $26.4918   $26.49   $26.50   $26.50  
  Purchase #3 $123.57   10.578%   $136.6412   $136.64   $136.65   $136.60  
  Purchase #4 $50.81   11.191%   $56.4961   $56.50   $56.50   $56.50  
  Purchase #5 $12.31   13.419%   $13.9619   $13.96   $13.95   $14.00  
  Purchase #6 $157.60   11.782%   $176.1684   $176.17   $176.15   $176.20  
  Purchase #7 $54.67   9.632%   $59.9358   $59.94   $59.95   $59.90  
  7 purchase totals = $511.31       $566.2945   $566.30   $566.30   $566.30