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 $60.67   12.501%   $68.2544   $68.25   $68.25   $68.30  
  Purchase #2 $215.78   5.820%   $228.3384   $228.34   $228.35   $228.30  
  Purchase #3 $98.44   10.380%   $108.6581   $108.66   $108.65   $108.70  
  Purchase #4 $129.25   9.646%   $141.7175   $141.72   $141.70   $141.70  
  Purchase #5 $187.26   10.318%   $206.5815   $206.58   $206.60   $206.60  
  Purchase #6 $155.60   8.183%   $168.3327   $168.33   $168.35   $168.30  
  Purchase #7 $107.97   7.289%   $115.8399   $115.84   $115.85   $115.80  
  7 purchase totals = $954.97       $1,037.7225   $1,037.72   $1,037.75   $1,037.70