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 $206.53   12.794%   $232.9534   $232.95   $232.95   $233.00  
  Purchase #2 $49.91   7.121%   $53.4641   $53.46   $53.45   $53.50  
  Purchase #3 $71.49   11.858%   $79.9673   $79.97   $79.95   $80.00  
  Purchase #4 $118.88   3.570%   $123.124   $123.12   $123.10   $123.10  
  Purchase #5 $200.32   13.423%   $227.209   $227.21   $227.20   $227.20  
  Purchase #6 $182.27   10.799%   $201.9533   $201.95   $201.95   $202.00  
  Purchase #7 $160.80   7.531%   $172.9098   $172.91   $172.90   $172.90  
  7 purchase totals = $990.20       $1,091.5809   $1,091.57   $1,091.50   $1,091.70