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 $216.67   13.811%   $246.5943   $246.59   $246.60   $246.60  
  Purchase #2 $22.64   9.556%   $24.8035   $24.80   $24.80   $24.80  
  Purchase #3 $157.98   12.461%   $177.6659   $177.67   $177.65   $177.70  
  Purchase #4 $186.34   4.867%   $195.4092   $195.41   $195.40   $195.40  
  Purchase #5 $249.76   11.737%   $279.0743   $279.07   $279.05   $279.10  
  Purchase #6 $219.75   5.264%   $231.3176   $231.32   $231.30   $231.30  
  Purchase #7 $186.33   11.385%   $207.5437   $207.54   $207.55   $207.50  
  7 purchase totals = $1,239.47       $1,362.4085   $1,362.40   $1,362.35   $1,362.40