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 $113.36   11.562%   $126.4667   $126.47   $126.45   $126.50  
  Purchase #2 $41.54   10.365%   $45.8456   $45.85   $45.85   $45.80  
  Purchase #3 $12.94   8.122%   $13.991   $13.99   $14.00   $14.00  
  Purchase #4 $241.36   4.724%   $252.7618   $252.76   $252.75   $252.80  
  Purchase #5 $210.30   5.563%   $221.999   $222.00   $222.00   $222.00  
  Purchase #6 $94.80   7.506%   $101.9157   $101.92   $101.90   $101.90  
  Purchase #7 $62.56   7.136%   $67.0243   $67.02   $67.00   $67.00  
  7 purchase totals = $776.86       $830.0041   $830.01   $829.95   $830.00