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 $207.45   12.463%   $233.3045   $233.30   $233.30   $233.30  
  Purchase #2 $17.31   11.314%   $19.2685   $19.27   $19.25   $19.30  
  Purchase #3 $182.26   4.257%   $190.0188   $190.02   $190.00   $190.00  
  Purchase #4 $143.55   12.139%   $160.9755   $160.98   $161.00   $161.00  
  Purchase #5 $221.96   6.301%   $235.9457   $235.95   $235.95   $235.90  
  Purchase #6 $101.29   10.625%   $112.0521   $112.05   $112.05   $112.10  
  Purchase #7 $191.87   12.469%   $215.7943   $215.79   $215.80   $215.80  
  7 purchase totals = $1,065.69       $1,167.3594   $1,167.36   $1,167.35   $1,167.40