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 $165.75   7.513%   $178.2028   $178.20   $178.20   $178.20  
  Purchase #2 $249.97   8.617%   $271.5099   $271.51   $271.50   $271.50  
  Purchase #3 $96.40   5.300%   $101.5092   $101.51   $101.50   $101.50  
  Purchase #4 $167.81   4.870%   $175.9823   $175.98   $176.00   $176.00  
  Purchase #5 $168.44   12.743%   $189.9043   $189.90   $189.90   $189.90  
  Purchase #6 $60.33   9.309%   $65.9461   $65.95   $65.95   $65.90  
  Purchase #7 $44.76   3.113%   $46.1534   $46.15   $46.15   $46.20  
  7 purchase totals = $953.46       $1,029.2080   $1,029.20   $1,029.20   $1,029.20