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 $22.61   6.484%   $24.076   $24.08   $24.10   $24.10  
  Purchase #2 $69.66   5.766%   $73.6766   $73.68   $73.70   $73.70  
  Purchase #3 $222.33   12.382%   $249.8589   $249.86   $249.85   $249.90  
  Purchase #4 $16.65   7.572%   $17.9107   $17.91   $17.90   $17.90  
  Purchase #5 $169.53   7.141%   $181.6361   $181.64   $181.65   $181.60  
  Purchase #6 $154.65   8.157%   $167.2648   $167.26   $167.25   $167.30  
  Purchase #7 $218.95   8.346%   $237.2236   $237.22   $237.20   $237.20  
  7 purchase totals = $874.38       $951.6467   $951.65   $951.65   $951.70