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 $21.95   12.148%   $24.6165   $24.62   $24.60   $24.60  
  Purchase #2 $65.83   4.553%   $68.8272   $68.83   $68.85   $68.80  
  Purchase #3 $212.42   12.254%   $238.4499   $238.45   $238.45   $238.40  
  Purchase #4 $245.58   13.407%   $278.5049   $278.50   $278.50   $278.50  
  Purchase #5 $64.32   8.198%   $69.593   $69.59   $69.60   $69.60  
  Purchase #6 $198.68   12.516%   $223.5468   $223.55   $223.55   $223.50  
  Purchase #7 $220.98   11.480%   $246.3485   $246.35   $246.35   $246.30  
  7 purchase totals = $1,029.76       $1,149.8868   $1,149.89   $1,149.90   $1,149.70