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 $45.76   13.855%   $52.1   $52.10   $52.10   $52.10  
  Purchase #2 $236.60   5.560%   $249.755   $249.76   $249.75   $249.80  
  Purchase #3 $119.94   11.360%   $133.5652   $133.57   $133.55   $133.60  
  Purchase #4 $122.66   3.573%   $127.0426   $127.04   $127.05   $127.00  
  Purchase #5 $54.63   10.171%   $60.1864   $60.19   $60.20   $60.20  
  Purchase #6 $140.25   3.741%   $145.4968   $145.50   $145.50   $145.50  
  Purchase #7 $207.46   12.695%   $233.797   $233.80   $233.80   $233.80  
  7 purchase totals = $927.30       $1,001.9430   $1,001.96   $1,001.95   $1,002.00