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 $211.55   3.195%   $218.309   $218.31   $218.30   $218.30  
  Purchase #2 $241.67   13.667%   $274.699   $274.70   $274.70   $274.70  
  Purchase #3 $79.46   12.205%   $89.1581   $89.16   $89.15   $89.20  
  Purchase #4 $211.85   9.632%   $232.2554   $232.26   $232.25   $232.30  
  Purchase #5 $82.62   13.789%   $94.0125   $94.01   $94.00   $94.00  
  Purchase #6 $96.93   7.192%   $103.9012   $103.90   $103.90   $103.90  
  Purchase #7 $79.83   9.243%   $87.2087   $87.21   $87.20   $87.20  
  7 purchase totals = $1,003.91       $1,099.5439   $1,099.55   $1,099.50   $1,099.60