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 $23.84   11.792%   $26.6512   $26.65   $26.65   $26.70  
  Purchase #2 $52.88   5.864%   $55.9809   $55.98   $56.00   $56.00  
  Purchase #3 $63.53   10.735%   $70.3499   $70.35   $70.35   $70.30  
  Purchase #4 $152.62   6.861%   $163.0913   $163.09   $163.10   $163.10  
  Purchase #5 $201.95   13.207%   $228.6215   $228.62   $228.60   $228.60  
  Purchase #6 $231.67   6.138%   $245.8899   $245.89   $245.90   $245.90  
  Purchase #7 $121.43   3.417%   $125.5793   $125.58   $125.60   $125.60  
  7 purchase totals = $847.92       $916.1640   $916.16   $916.20   $916.20