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 $65.79   8.749%   $71.546   $71.55   $71.55   $71.50  
  Purchase #2 $248.40   13.439%   $281.7825   $281.78   $281.80   $281.80  
  Purchase #3 $151.28   11.314%   $168.3958   $168.40   $168.40   $168.40  
  Purchase #4 $47.58   5.850%   $50.3634   $50.36   $50.35   $50.40  
  Purchase #5 $206.96   11.415%   $230.5845   $230.58   $230.60   $230.60  
  Purchase #6 $111.79   11.755%   $124.9309   $124.93   $124.95   $124.90  
  Purchase #7 $78.59   7.615%   $84.5746   $84.57   $84.55   $84.60  
  7 purchase totals = $910.39       $1,012.1777   $1,012.17   $1,012.20   $1,012.20