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 $216.43   12.647%   $243.8019   $243.80   $243.80   $243.80  
  Purchase #2 $42.42   9.224%   $46.3328   $46.33   $46.35   $46.30  
  Purchase #3 $133.56   6.873%   $142.7396   $142.74   $142.75   $142.70  
  Purchase #4 $156.78   6.577%   $167.0914   $167.09   $167.10   $167.10  
  Purchase #5 $187.28   10.706%   $207.3302   $207.33   $207.35   $207.30  
  Purchase #6 $242.77   7.204%   $260.2592   $260.26   $260.25   $260.30  
  Purchase #7 $142.85   6.351%   $151.9224   $151.92   $151.90   $151.90  
  7 purchase totals = $1,122.09       $1,219.4775   $1,219.47   $1,219.50   $1,219.40