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 $32.77   11.374%   $36.4973   $36.50   $36.50   $36.50  
  Purchase #2 $61.64   12.839%   $69.554   $69.55   $69.55   $69.60  
  Purchase #3 $6.36   11.565%   $7.0955   $7.10   $7.10   $7.10  
  Purchase #4 $220.91   6.646%   $235.5917   $235.59   $235.60   $235.60  
  Purchase #5 $218.49   6.328%   $232.316   $232.32   $232.30   $232.30  
  Purchase #6 $199.90   3.665%   $207.2263   $207.23   $207.25   $207.20  
  Purchase #7 $206.37   11.864%   $230.8537   $230.85   $230.85   $230.90  
  7 purchase totals = $946.44       $1,019.1345   $1,019.14   $1,019.15   $1,019.20