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 $31.76   10.149%   $34.9833   $34.98   $35.00   $35.00  
  Purchase #2 $242.62   4.400%   $253.2953   $253.30   $253.30   $253.30  
  Purchase #3 $69.70   10.208%   $76.815   $76.82   $76.80   $76.80  
  Purchase #4 $137.94   13.151%   $156.0805   $156.08   $156.10   $156.10  
  Purchase #5 $138.41   6.813%   $147.8399   $147.84   $147.85   $147.80  
  Purchase #6 $187.42   4.658%   $196.15   $196.15   $196.15   $196.20  
  Purchase #7 $161.35   5.489%   $170.2065   $170.21   $170.20   $170.20  
  7 purchase totals = $969.20       $1,035.3705   $1,035.38   $1,035.40   $1,035.40