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 $154.71   8.363%   $167.6484   $167.65   $167.65   $167.60  
  Purchase #2 $245.50   10.661%   $271.6728   $271.67   $271.65   $271.70  
  Purchase #3 $211.55   6.832%   $226.0031   $226.00   $226.00   $226.00  
  Purchase #4 $50.68   7.258%   $54.3584   $54.36   $54.35   $54.40  
  Purchase #5 $84.65   7.219%   $90.7609   $90.76   $90.75   $90.80  
  Purchase #6 $77.81   8.324%   $84.2869   $84.29   $84.30   $84.30  
  Purchase #7 $98.73   13.246%   $111.8078   $111.81   $111.80   $111.80  
  7 purchase totals = $923.63       $1,006.5383   $1,006.54   $1,006.50   $1,006.60