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 $46.57   13.609%   $52.9077   $52.91   $52.90   $52.90  
  Purchase #2 $76.70   10.630%   $84.8532   $84.85   $84.85   $84.90  
  Purchase #3 $170.25   12.801%   $192.0437   $192.04   $192.05   $192.00  
  Purchase #4 $155.99   7.623%   $167.8811   $167.88   $167.90   $167.90  
  Purchase #5 $120.72   13.813%   $137.3951   $137.40   $137.40   $137.40  
  Purchase #6 $231.67   12.264%   $260.082   $260.08   $260.10   $260.10  
  Purchase #7 $162.34   10.123%   $178.7737   $178.77   $178.75   $178.80  
  7 purchase totals = $964.24       $1,073.9365   $1,073.93   $1,073.95   $1,074.00