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 $61.73   9.646%   $67.6845   $67.68   $67.70   $67.70  
  Purchase #2 $232.87   7.809%   $251.0548   $251.05   $251.05   $251.10  
  Purchase #3 $107.85   9.856%   $118.4797   $118.48   $118.50   $118.50  
  Purchase #4 $29.66   12.260%   $33.2963   $33.30   $33.30   $33.30  
  Purchase #5 $189.60   9.182%   $207.0091   $207.01   $207.00   $207.00  
  Purchase #6 $20.36   9.638%   $22.3223   $22.32   $22.30   $22.30  
  Purchase #7 $137.90   4.278%   $143.7994   $143.80   $143.80   $143.80  
  7 purchase totals = $779.97       $843.6461   $843.64   $843.65   $843.70