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 $53.65   6.631%   $57.2075   $57.21   $57.20   $57.20  
  Purchase #2 $95.37   6.724%   $101.7827   $101.78   $101.80   $101.80  
  Purchase #3 $120.98   3.147%   $124.7872   $124.79   $124.80   $124.80  
  Purchase #4 $209.60   7.341%   $224.9867   $224.99   $225.00   $225.00  
  Purchase #5 $187.73   11.109%   $208.5849   $208.58   $208.60   $208.60  
  Purchase #6 $37.43   9.511%   $40.99   $40.99   $41.00   $41.00  
  Purchase #7 $128.88   4.449%   $134.6139   $134.61   $134.60   $134.60  
  7 purchase totals = $833.64       $892.9529   $892.95   $893.00   $893.00