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 $66.57   7.662%   $71.6706   $71.67   $71.65   $71.70  
  Purchase #2 $147.44   4.695%   $154.3623   $154.36   $154.35   $154.40  
  Purchase #3 $73.34   11.791%   $81.9875   $81.99   $82.00   $82.00  
  Purchase #4 $183.35   11.243%   $203.964   $203.96   $203.95   $204.00  
  Purchase #5 $229.90   9.602%   $251.975   $251.98   $252.00   $252.00  
  Purchase #6 $138.54   9.212%   $151.3023   $151.30   $151.30   $151.30  
  Purchase #7 $206.68   8.871%   $225.0146   $225.01   $225.00   $225.00  
  7 purchase totals = $1,045.82       $1,140.2763   $1,140.27   $1,140.25   $1,140.40