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 $219.62   7.493%   $236.0761   $236.08   $236.10   $236.10  
  Purchase #2 $204.66   13.533%   $232.3566   $232.36   $232.35   $232.40  
  Purchase #3 $60.50   4.592%   $63.2782   $63.28   $63.30   $63.30  
  Purchase #4 $187.77   12.682%   $211.583   $211.58   $211.60   $211.60  
  Purchase #5 $70.38   4.408%   $73.4824   $73.48   $73.50   $73.50  
  Purchase #6 $217.74   13.792%   $247.7707   $247.77   $247.75   $247.80  
  Purchase #7 $245.56   5.543%   $259.1714   $259.17   $259.15   $259.20  
  7 purchase totals = $1,206.23       $1,323.7184   $1,323.72   $1,323.75   $1,323.90