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 $94.34   9.221%   $103.0391   $103.04   $103.05   $103.00  
  Purchase #2 $162.56   13.269%   $184.1301   $184.13   $184.15   $184.10  
  Purchase #3 $142.80   13.622%   $162.2522   $162.25   $162.25   $162.30  
  Purchase #4 $54.34   4.803%   $56.95   $56.95   $56.95   $57.00  
  Purchase #5 $136.96   13.560%   $155.5318   $155.53   $155.55   $155.50  
  Purchase #6 $226.75   11.728%   $253.3432   $253.34   $253.35   $253.30  
  Purchase #7 $113.95   4.172%   $118.704   $118.70   $118.70   $118.70  
  7 purchase totals = $931.70       $1,033.9504   $1,033.94   $1,034.00   $1,033.90