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 $214.99   8.819%   $233.95   $233.95   $233.95   $234.00  
  Purchase #2 $155.29   6.460%   $165.3217   $165.32   $165.30   $165.30  
  Purchase #3 $10.85   10.635%   $12.0039   $12.00   $12.00   $12.00  
  Purchase #4 $213.57   11.152%   $237.3873   $237.39   $237.40   $237.40  
  Purchase #5 $52.44   8.322%   $56.8041   $56.80   $56.80   $56.80  
  Purchase #6 $177.42   6.777%   $189.4438   $189.44   $189.45   $189.40  
  Purchase #7 $169.42   12.300%   $190.2587   $190.26   $190.25   $190.30  
  7 purchase totals = $993.98       $1,085.1695   $1,085.16   $1,085.15   $1,085.20