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 $169.54   8.285%   $183.5864   $183.59   $183.60   $183.60  
  Purchase #2 $119.25   13.124%   $134.9004   $134.90   $134.90   $134.90  
  Purchase #3 $8.92   11.386%   $9.9356   $9.94   $9.95   $9.90  
  Purchase #4 $24.29   12.419%   $27.3066   $27.31   $27.30   $27.30  
  Purchase #5 $202.49   9.164%   $221.0462   $221.05   $221.05   $221.00  
  Purchase #6 $119.95   9.399%   $131.2241   $131.22   $131.20   $131.20  
  Purchase #7 $172.65   10.361%   $190.5383   $190.54   $190.55   $190.50  
  7 purchase totals = $817.09       $898.5376   $898.55   $898.55   $898.40