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 $50.50   11.829%   $56.4736   $56.47   $56.45   $56.50  
  Purchase #2 $218.65   9.426%   $239.2599   $239.26   $239.25   $239.30  
  Purchase #3 $116.81   10.450%   $129.0166   $129.02   $129.00   $129.00  
  Purchase #4 $72.90   4.687%   $76.3168   $76.32   $76.30   $76.30  
  Purchase #5 $236.52   7.645%   $254.602   $254.60   $254.60   $254.60  
  Purchase #6 $114.35   4.705%   $119.7302   $119.73   $119.75   $119.70  
  Purchase #7 $134.41   12.400%   $151.0768   $151.08   $151.10   $151.10  
  7 purchase totals = $944.14       $1,026.4759   $1,026.48   $1,026.45   $1,026.50