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 $32.87   8.258%   $35.5844   $35.58   $35.60   $35.60  
  Purchase #2 $194.87   7.835%   $210.1381   $210.14   $210.15   $210.10  
  Purchase #3 $204.74   8.468%   $222.0774   $222.08   $222.10   $222.10  
  Purchase #4 $229.94   11.385%   $256.1187   $256.12   $256.10   $256.10  
  Purchase #5 $206.28   3.376%   $213.244   $213.24   $213.25   $213.20  
  Purchase #6 $169.75   9.541%   $185.9458   $185.95   $185.95   $185.90  
  Purchase #7 $147.27   3.671%   $152.6763   $152.68   $152.70   $152.70  
  7 purchase totals = $1,185.72       $1,275.7847   $1,275.79   $1,275.85   $1,275.70