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 $49.83   12.767%   $56.1918   $56.19   $56.20   $56.20  
  Purchase #2 $207.79   5.870%   $219.9873   $219.99   $220.00   $220.00  
  Purchase #3 $145.40   8.443%   $157.6761   $157.68   $157.70   $157.70  
  Purchase #4 $231.92   7.572%   $249.481   $249.48   $249.50   $249.50  
  Purchase #5 $56.94   3.607%   $58.9938   $58.99   $59.00   $59.00  
  Purchase #6 $220.76   10.380%   $243.6749   $243.67   $243.65   $243.70  
  Purchase #7 $105.96   13.441%   $120.2021   $120.20   $120.20   $120.20  
  7 purchase totals = $1,018.60       $1,106.2070   $1,106.20   $1,106.25   $1,106.30