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 $224.49   7.811%   $242.0249   $242.02   $242.00   $242.00  
  Purchase #2 $101.82   11.270%   $113.2951   $113.30   $113.30   $113.30  
  Purchase #3 $136.58   11.125%   $151.7745   $151.77   $151.75   $151.80  
  Purchase #4 $42.72   9.509%   $46.7822   $46.78   $46.80   $46.80  
  Purchase #5 $52.94   12.295%   $59.449   $59.45   $59.45   $59.40  
  Purchase #6 $80.90   4.481%   $84.5251   $84.53   $84.55   $84.50  
  Purchase #7 $59.64   3.694%   $61.8431   $61.84   $61.85   $61.80  
  7 purchase totals = $699.09       $759.6939   $759.69   $759.70   $759.60