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 $68.59   7.164%   $73.5038   $73.50   $73.50   $73.50  
  Purchase #2 $69.29   6.359%   $73.6962   $73.70   $73.70   $73.70  
  Purchase #3 $135.51   13.321%   $153.5613   $153.56   $153.55   $153.60  
  Purchase #4 $106.61   4.613%   $111.5279   $111.53   $111.55   $111.50  
  Purchase #5 $106.88   11.734%   $119.4213   $119.42   $119.40   $119.40  
  Purchase #6 $166.55   11.699%   $186.0347   $186.03   $186.05   $186.00  
  Purchase #7 $230.86   10.418%   $254.911   $254.91   $254.90   $254.90  
  7 purchase totals = $884.29       $972.6562   $972.65   $972.65   $972.60