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 $146.38   10.309%   $161.4703   $161.47   $161.45   $161.50  
  Purchase #2 $31.33   3.144%   $32.315   $32.32   $32.30   $32.30  
  Purchase #3 $168.92   4.364%   $176.2917   $176.29   $176.30   $176.30  
  Purchase #4 $43.35   11.167%   $48.1909   $48.19   $48.20   $48.20  
  Purchase #5 $114.95   9.628%   $126.0174   $126.02   $126.00   $126.00  
  Purchase #6 $250.65   11.197%   $278.7153   $278.72   $278.70   $278.70  
  Purchase #7 $205.74   4.606%   $215.2164   $215.22   $215.20   $215.20  
  7 purchase totals = $961.32       $1,038.2170   $1,038.23   $1,038.15   $1,038.20