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 $23.76   9.426%   $25.9996   $26.00   $26.00   $26.00  
  Purchase #2 $116.51   7.238%   $124.943   $124.94   $124.95   $124.90  
  Purchase #3 $16.32   7.800%   $17.593   $17.59   $17.60   $17.60  
  Purchase #4 $96.33   7.741%   $103.7869   $103.79   $103.80   $103.80  
  Purchase #5 $240.80   11.563%   $268.6437   $268.64   $268.65   $268.60  
  Purchase #6 $117.48   7.320%   $126.0795   $126.08   $126.10   $126.10  
  Purchase #7 $218.78   7.820%   $235.8886   $235.89   $235.90   $235.90  
  7 purchase totals = $829.98       $902.9343   $902.93   $903.00   $902.90