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 $249.83   6.671%   $266.4962   $266.50   $266.50   $266.50  
  Purchase #2 $150.66   13.863%   $171.546   $171.55   $171.55   $171.50  
  Purchase #3 $53.42   9.349%   $58.4142   $58.41   $58.40   $58.40  
  Purchase #4 $212.79   3.284%   $219.778   $219.78   $219.80   $219.80  
  Purchase #5 $97.59   8.186%   $105.5787   $105.58   $105.60   $105.60  
  Purchase #6 $111.25   6.199%   $118.1464   $118.15   $118.15   $118.10  
  Purchase #7 $77.28   13.444%   $87.6695   $87.67   $87.65   $87.70  
  7 purchase totals = $952.82       $1,027.6290   $1,027.64   $1,027.65   $1,027.60