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 $137.44   4.295%   $143.343   $143.34   $143.35   $143.30  
  Purchase #2 $137.54   9.670%   $150.8401   $150.84   $150.85   $150.80  
  Purchase #3 $121.61   12.170%   $136.4099   $136.41   $136.40   $136.40  
  Purchase #4 $17.38   3.716%   $18.0258   $18.03   $18.05   $18.00  
  Purchase #5 $226.74   11.446%   $252.6927   $252.69   $252.70   $252.70  
  Purchase #6 $105.30   13.237%   $119.2386   $119.24   $119.25   $119.20  
  Purchase #7 $243.68   7.739%   $262.5384   $262.54   $262.55   $262.50  
  7 purchase totals = $989.69       $1,083.0885   $1,083.09   $1,083.15   $1,082.90