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 $218.33   9.302%   $238.6391   $238.64   $238.65   $238.60  
  Purchase #2 $212.56   12.740%   $239.6401   $239.64   $239.65   $239.60  
  Purchase #3 $85.32   12.832%   $96.2683   $96.27   $96.25   $96.30  
  Purchase #4 $225.39   7.559%   $242.4272   $242.43   $242.45   $242.40  
  Purchase #5 $248.31   11.741%   $277.4641   $277.46   $277.45   $277.50  
  Purchase #6 $57.95   8.673%   $62.976   $62.98   $63.00   $63.00  
  Purchase #7 $76.34   7.449%   $82.0266   $82.03   $82.05   $82.00  
  7 purchase totals = $1,124.20       $1,239.4414   $1,239.45   $1,239.50   $1,239.40