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 $93.25   3.598%   $96.6051   $96.61   $96.60   $96.60  
  Purchase #2 $228.29   9.397%   $249.7424   $249.74   $249.75   $249.70  
  Purchase #3 $65.86   3.233%   $67.9893   $67.99   $68.00   $68.00  
  Purchase #4 $228.76   12.379%   $257.0782   $257.08   $257.10   $257.10  
  Purchase #5 $94.90   12.119%   $106.4009   $106.40   $106.40   $106.40  
  Purchase #6 $193.79   10.393%   $213.9306   $213.93   $213.95   $213.90  
  Purchase #7 $80.96   10.524%   $89.4802   $89.48   $89.50   $89.50  
  7 purchase totals = $985.81       $1,081.2267   $1,081.23   $1,081.30   $1,081.20