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 $58.99   7.833%   $63.6107   $63.61   $63.60   $63.60  
  Purchase #2 $207.48   3.557%   $214.8601   $214.86   $214.85   $214.90  
  Purchase #3 $147.49   4.479%   $154.0961   $154.10   $154.10   $154.10  
  Purchase #4 $93.91   3.241%   $96.9536   $96.95   $96.95   $97.00  
  Purchase #5 $135.72   5.482%   $143.1602   $143.16   $143.15   $143.20  
  Purchase #6 $81.32   5.164%   $85.5194   $85.52   $85.50   $85.50  
  Purchase #7 $83.60   13.183%   $94.621   $94.62   $94.60   $94.60  
  7 purchase totals = $808.51       $852.8211   $852.82   $852.75   $852.90