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 $82.73   12.212%   $92.833   $92.83   $92.85   $92.80  
  Purchase #2 $150.35   8.764%   $163.5267   $163.53   $163.55   $163.50  
  Purchase #3 $76.54   4.778%   $80.1971   $80.20   $80.20   $80.20  
  Purchase #4 $238.76   8.801%   $259.7733   $259.77   $259.75   $259.80  
  Purchase #5 $99.40   3.567%   $102.9456   $102.95   $102.95   $102.90  
  Purchase #6 $165.54   6.684%   $176.6047   $176.60   $176.60   $176.60  
  Purchase #7 $180.64   4.232%   $188.2847   $188.28   $188.30   $188.30  
  7 purchase totals = $993.96       $1,064.1651   $1,064.16   $1,064.20   $1,064.10