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 $49.29   7.696%   $53.0834   $53.08   $53.10   $53.10  
  Purchase #2 $250.81   9.743%   $275.2464   $275.25   $275.25   $275.20  
  Purchase #3 $176.43   9.204%   $192.6686   $192.67   $192.65   $192.70  
  Purchase #4 $115.99   8.644%   $126.0162   $126.02   $126.00   $126.00  
  Purchase #5 $70.60   8.118%   $76.3313   $76.33   $76.35   $76.30  
  Purchase #6 $205.38   7.845%   $221.4921   $221.49   $221.50   $221.50  
  Purchase #7 $138.75   11.673%   $154.9463   $154.95   $154.95   $154.90  
  7 purchase totals = $1,007.25       $1,099.7843   $1,099.79   $1,099.80   $1,099.70