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 $237.66   6.566%   $253.2648   $253.26   $253.25   $253.30  
  Purchase #2 $136.38   3.341%   $140.9365   $140.94   $140.95   $140.90  
  Purchase #3 $92.97   9.196%   $101.5195   $101.52   $101.50   $101.50  
  Purchase #4 $236.75   11.305%   $263.5146   $263.51   $263.50   $263.50  
  Purchase #5 $124.89   8.506%   $135.5131   $135.51   $135.50   $135.50  
  Purchase #6 $241.50   9.347%   $264.073   $264.07   $264.05   $264.10  
  Purchase #7 $173.92   7.219%   $186.4753   $186.48   $186.50   $186.50  
  7 purchase totals = $1,244.07       $1,345.2968   $1,345.29   $1,345.25   $1,345.30