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 $247.36   8.260%   $267.7919   $267.79   $267.80   $267.80  
  Purchase #2 $146.62   11.811%   $163.9373   $163.94   $163.95   $163.90  
  Purchase #3 $118.25   13.107%   $133.749   $133.75   $133.75   $133.70  
  Purchase #4 $18.50   12.228%   $20.7622   $20.76   $20.75   $20.80  
  Purchase #5 $129.94   8.304%   $140.7302   $140.73   $140.75   $140.70  
  Purchase #6 $175.30   4.289%   $182.8186   $182.82   $182.80   $182.80  
  Purchase #7 $141.58   7.573%   $152.3019   $152.30   $152.30   $152.30  
  7 purchase totals = $977.55       $1,062.0911   $1,062.09   $1,062.10   $1,062.00