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 $108.44   10.364%   $119.6787   $119.68   $119.70   $119.70  
  Purchase #2 $234.36   9.676%   $257.0367   $257.04   $257.05   $257.00  
  Purchase #3 $16.52   11.143%   $18.3608   $18.36   $18.35   $18.40  
  Purchase #4 $129.58   3.328%   $133.8924   $133.89   $133.90   $133.90  
  Purchase #5 $153.81   6.767%   $164.2183   $164.22   $164.20   $164.20  
  Purchase #6 $173.64   12.534%   $195.404   $195.40   $195.40   $195.40  
  Purchase #7 $69.34   4.753%   $72.6357   $72.64   $72.65   $72.60  
  7 purchase totals = $885.69       $961.2266   $961.23   $961.25   $961.20