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 $72.28   12.683%   $81.4473   $81.45   $81.45   $81.40  
  Purchase #2 $158.59   5.452%   $167.2363   $167.24   $167.25   $167.20  
  Purchase #3 $192.80   5.103%   $202.6386   $202.64   $202.65   $202.60  
  Purchase #4 $16.43   3.436%   $16.9945   $16.99   $17.00   $17.00  
  Purchase #5 $212.74   10.670%   $235.4394   $235.44   $235.45   $235.40  
  Purchase #6 $238.44   11.389%   $265.5959   $265.60   $265.60   $265.60  
  Purchase #7 $76.81   13.439%   $87.1325   $87.13   $87.15   $87.10  
  7 purchase totals = $968.09       $1,056.4845   $1,056.49   $1,056.55   $1,056.30