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 $7.76   4.483%   $8.1079   $8.11   $8.10   $8.10  
  Purchase #2 $145.99   9.311%   $159.5831   $159.58   $159.60   $159.60  
  Purchase #3 $114.50   6.123%   $121.5108   $121.51   $121.50   $121.50  
  Purchase #4 $23.85   5.865%   $25.2488   $25.25   $25.25   $25.20  
  Purchase #5 $157.29   5.346%   $165.6987   $165.70   $165.70   $165.70  
  Purchase #6 $5.48   8.368%   $5.9386   $5.94   $5.95   $5.90  
  Purchase #7 $133.78   13.426%   $151.7413   $151.74   $151.75   $151.70  
  7 purchase totals = $588.65       $637.8292   $637.83   $637.85   $637.70