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 $230.65   11.841%   $257.9613   $257.96   $257.95   $258.00  
  Purchase #2 $115.75   7.243%   $124.1338   $124.13   $124.15   $124.10  
  Purchase #3 $240.29   11.572%   $268.0964   $268.10   $268.10   $268.10  
  Purchase #4 $87.49   6.857%   $93.4892   $93.49   $93.50   $93.50  
  Purchase #5 $7.44   12.640%   $8.3804   $8.38   $8.40   $8.40  
  Purchase #6 $113.25   8.597%   $122.9861   $122.99   $123.00   $123.00  
  Purchase #7 $136.74   10.847%   $151.5722   $151.57   $151.55   $151.60  
  7 purchase totals = $931.61       $1,026.6194   $1,026.62   $1,026.65   $1,026.70