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 $212.83   12.315%   $239.04   $239.04   $239.05   $239.00  
  Purchase #2 $72.26   3.456%   $74.7573   $74.76   $74.75   $74.80  
  Purchase #3 $151.62   12.133%   $170.0161   $170.02   $170.00   $170.00  
  Purchase #4 $241.82   9.136%   $263.9127   $263.91   $263.90   $263.90  
  Purchase #5 $106.56   6.229%   $113.1976   $113.20   $113.20   $113.20  
  Purchase #6 $67.36   9.356%   $73.6622   $73.66   $73.65   $73.70  
  Purchase #7 $12.35   4.737%   $12.935   $12.94   $12.95   $12.90  
  7 purchase totals = $864.80       $947.5209   $947.53   $947.50   $947.50