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 $58.52   3.438%   $60.5319   $60.53   $60.55   $60.50  
  Purchase #2 $245.88   8.587%   $266.9937   $266.99   $267.00   $267.00  
  Purchase #3 $129.80   11.203%   $144.3415   $144.34   $144.35   $144.30  
  Purchase #4 $243.83   3.416%   $252.1592   $252.16   $252.15   $252.20  
  Purchase #5 $224.52   3.360%   $232.0639   $232.06   $232.05   $232.10  
  Purchase #6 $146.35   3.792%   $151.8996   $151.90   $151.90   $151.90  
  Purchase #7 $79.32   6.865%   $84.7653   $84.77   $84.75   $84.80  
  7 purchase totals = $1,128.22       $1,192.7551   $1,192.75   $1,192.75   $1,192.80