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 $22.69   3.341%   $23.4481   $23.45   $23.45   $23.40  
  Purchase #2 $103.53   9.497%   $113.3622   $113.36   $113.35   $113.40  
  Purchase #3 $143.37   6.709%   $152.9887   $152.99   $153.00   $153.00  
  Purchase #4 $99.53   12.449%   $111.9205   $111.92   $111.90   $111.90  
  Purchase #5 $245.80   12.401%   $276.2817   $276.28   $276.30   $276.30  
  Purchase #6 $111.58   7.421%   $119.8604   $119.86   $119.85   $119.90  
  Purchase #7 $238.25   11.434%   $265.4915   $265.49   $265.50   $265.50  
  7 purchase totals = $964.75       $1,063.3531   $1,063.35   $1,063.35   $1,063.40