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 $67.75   4.792%   $70.9966   $71.00   $71.00   $71.00  
  Purchase #2 $240.98   13.257%   $272.9267   $272.93   $272.95   $272.90  
  Purchase #3 $242.69   4.106%   $252.6549   $252.65   $252.65   $252.70  
  Purchase #4 $190.99   9.848%   $209.7987   $209.80   $209.80   $209.80  
  Purchase #5 $218.44   12.589%   $245.9394   $245.94   $245.95   $245.90  
  Purchase #6 $149.48   5.754%   $158.0811   $158.08   $158.10   $158.10  
  Purchase #7 $105.55   12.511%   $118.7554   $118.76   $118.75   $118.80  
  7 purchase totals = $1,215.88       $1,329.1528   $1,329.16   $1,329.20   $1,329.20