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 $32.74   6.689%   $34.93   $34.93   $34.95   $34.90  
  Purchase #2 $59.62   12.768%   $67.2323   $67.23   $67.25   $67.20  
  Purchase #3 $126.68   3.337%   $130.9073   $130.91   $130.90   $130.90  
  Purchase #4 $105.38   3.155%   $108.7047   $108.70   $108.70   $108.70  
  Purchase #5 $112.76   10.711%   $124.8377   $124.84   $124.85   $124.80  
  Purchase #6 $141.45   10.471%   $156.2612   $156.26   $156.25   $156.30  
  Purchase #7 $124.33   10.750%   $137.6955   $137.70   $137.70   $137.70  
  7 purchase totals = $702.96       $760.5687   $760.57   $760.60   $760.50