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 $89.88   7.601%   $96.7118   $96.71   $96.70   $96.70  
  Purchase #2 $163.83   12.409%   $184.1597   $184.16   $184.15   $184.20  
  Purchase #3 $158.96   5.442%   $167.6106   $167.61   $167.60   $167.60  
  Purchase #4 $240.40   8.596%   $261.0648   $261.06   $261.05   $261.10  
  Purchase #5 $108.68   6.362%   $115.5942   $115.59   $115.60   $115.60  
  Purchase #6 $147.59   3.315%   $152.4826   $152.48   $152.50   $152.50  
  Purchase #7 $78.67   10.615%   $87.0208   $87.02   $87.00   $87.00  
  7 purchase totals = $988.01       $1,064.6445   $1,064.63   $1,064.60   $1,064.70