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 $161.91   3.149%   $167.0085   $167.01   $167.00   $167.00  
  Purchase #2 $74.66   12.108%   $83.6998   $83.70   $83.70   $83.70  
  Purchase #3 $108.26   11.259%   $120.449   $120.45   $120.45   $120.40  
  Purchase #4 $10.46   7.602%   $11.2552   $11.26   $11.25   $11.30  
  Purchase #5 $219.40   9.872%   $241.0592   $241.06   $241.05   $241.10  
  Purchase #6 $218.35   11.385%   $243.2091   $243.21   $243.20   $243.20  
  Purchase #7 $173.62   5.203%   $182.6534   $182.65   $182.65   $182.70  
  7 purchase totals = $966.66       $1,049.3342   $1,049.34   $1,049.30   $1,049.40