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 $234.34   8.393%   $254.0082   $254.01   $254.00   $254.00  
  Purchase #2 $23.49   3.118%   $24.2224   $24.22   $24.20   $24.20  
  Purchase #3 $246.79   7.646%   $265.6596   $265.66   $265.65   $265.70  
  Purchase #4 $196.55   3.279%   $202.9949   $202.99   $203.00   $203.00  
  Purchase #5 $68.62   6.463%   $73.0549   $73.05   $73.05   $73.10  
  Purchase #6 $184.81   5.116%   $194.2649   $194.26   $194.25   $194.30  
  Purchase #7 $23.30   10.369%   $25.716   $25.72   $25.70   $25.70  
  7 purchase totals = $977.90       $1,039.9209   $1,039.91   $1,039.85   $1,040.00