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 $60.50   10.715%   $66.9826   $66.98   $67.00   $67.00  
  Purchase #2 $60.58   11.653%   $67.6394   $67.64   $67.65   $67.60  
  Purchase #3 $148.54   6.782%   $158.614   $158.61   $158.60   $158.60  
  Purchase #4 $60.36   11.574%   $67.3461   $67.35   $67.35   $67.30  
  Purchase #5 $245.93   10.586%   $271.9641   $271.96   $271.95   $272.00  
  Purchase #6 $135.55   6.218%   $143.9785   $143.98   $144.00   $144.00  
  Purchase #7 $130.75   7.496%   $140.551   $140.55   $140.55   $140.60  
  7 purchase totals = $842.21       $917.0757   $917.07   $917.10   $917.10