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 $56.67   8.865%   $61.6938   $61.69   $61.70   $61.70  
  Purchase #2 $5.38   3.561%   $5.5716   $5.57   $5.55   $5.60  
  Purchase #3 $75.31   11.594%   $84.0414   $84.04   $84.05   $84.00  
  Purchase #4 $79.38   3.710%   $82.325   $82.33   $82.35   $82.30  
  Purchase #5 $59.47   4.134%   $61.9285   $61.93   $61.95   $61.90  
  Purchase #6 $120.44   8.558%   $130.7473   $130.75   $130.75   $130.70  
  Purchase #7 $213.61   7.692%   $230.0409   $230.04   $230.05   $230.00  
  7 purchase totals = $610.26       $656.3485   $656.35   $656.40   $656.20