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 $64.68   7.573%   $69.5782   $69.58   $69.60   $69.60  
  Purchase #2 $139.33   9.594%   $152.6973   $152.70   $152.70   $152.70  
  Purchase #3 $187.92   9.258%   $205.3176   $205.32   $205.30   $205.30  
  Purchase #4 $74.58   12.246%   $83.7131   $83.71   $83.70   $83.70  
  Purchase #5 $191.61   5.157%   $201.4913   $201.49   $201.50   $201.50  
  Purchase #6 $142.95   3.267%   $147.6202   $147.62   $147.60   $147.60  
  Purchase #7 $88.49   11.209%   $98.4088   $98.41   $98.40   $98.40  
  7 purchase totals = $889.56       $958.8265   $958.83   $958.80   $958.80