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 $64.69   13.759%   $73.5907   $73.59   $73.60   $73.60  
  Purchase #2 $97.36   8.295%   $105.436   $105.44   $105.45   $105.40  
  Purchase #3 $188.56   4.847%   $197.6995   $197.70   $197.70   $197.70  
  Purchase #4 $121.40   9.182%   $132.5469   $132.55   $132.55   $132.50  
  Purchase #5 $135.97   8.112%   $146.9999   $147.00   $147.00   $147.00  
  Purchase #6 $156.89   6.795%   $167.5507   $167.55   $167.55   $167.60  
  Purchase #7 $226.69   11.364%   $252.4511   $252.45   $252.45   $252.50  
  7 purchase totals = $991.56       $1,076.2748   $1,076.28   $1,076.30   $1,076.30