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 $110.93   6.831%   $118.5076   $118.51   $118.50   $118.50  
  Purchase #2 $56.46   9.264%   $61.6905   $61.69   $61.70   $61.70  
  Purchase #3 $161.58   3.385%   $167.0495   $167.05   $167.05   $167.00  
  Purchase #4 $182.36   13.458%   $206.902   $206.90   $206.90   $206.90  
  Purchase #5 $218.84   13.151%   $247.6196   $247.62   $247.60   $247.60  
  Purchase #6 $17.74   6.539%   $18.9   $18.90   $18.90   $18.90  
  Purchase #7 $144.30   5.391%   $152.0792   $152.08   $152.10   $152.10  
  7 purchase totals = $892.21       $972.7484   $972.75   $972.75   $972.70