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 $96.54   10.159%   $106.3475   $106.35   $106.35   $106.30  
  Purchase #2 $96.89   11.509%   $108.0411   $108.04   $108.05   $108.00  
  Purchase #3 $118.94   4.798%   $124.6467   $124.65   $124.65   $124.60  
  Purchase #4 $127.45   6.205%   $135.3583   $135.36   $135.35   $135.40  
  Purchase #5 $96.93   4.470%   $101.2628   $101.26   $101.25   $101.30  
  Purchase #6 $53.79   12.685%   $60.6133   $60.61   $60.60   $60.60  
  Purchase #7 $150.75   6.617%   $160.7251   $160.73   $160.75   $160.70  
  7 purchase totals = $741.29       $796.9948   $797.00   $797.00   $796.90