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 $67.68   12.456%   $76.1102   $76.11   $76.10   $76.10  
  Purchase #2 $224.91   5.688%   $237.7029   $237.70   $237.70   $237.70  
  Purchase #3 $139.51   4.171%   $145.329   $145.33   $145.35   $145.30  
  Purchase #4 $222.29   13.643%   $252.617   $252.62   $252.60   $252.60  
  Purchase #5 $7.29   9.676%   $7.9954   $8.00   $8.00   $8.00  
  Purchase #6 $44.71   11.669%   $49.9272   $49.93   $49.95   $49.90  
  Purchase #7 $167.89   13.409%   $190.4024   $190.40   $190.40   $190.40  
  7 purchase totals = $874.28       $960.0841   $960.09   $960.10   $960.00