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 $81.31   6.173%   $86.3293   $86.33   $86.35   $86.30  
  Purchase #2 $224.40   10.227%   $247.3494   $247.35   $247.35   $247.30  
  Purchase #3 $190.44   5.620%   $201.1427   $201.14   $201.15   $201.10  
  Purchase #4 $197.61   10.844%   $219.0388   $219.04   $219.05   $219.00  
  Purchase #5 $105.96   11.143%   $117.7671   $117.77   $117.75   $117.80  
  Purchase #6 $79.76   6.181%   $84.69   $84.69   $84.70   $84.70  
  Purchase #7 $245.94   6.827%   $262.7303   $262.73   $262.75   $262.70  
  7 purchase totals = $1,125.42       $1,219.0476   $1,219.05   $1,219.10   $1,218.90