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 $49.91   7.357%   $53.5819   $53.58   $53.60   $53.60  
  Purchase #2 $68.98   10.222%   $76.0311   $76.03   $76.05   $76.00  
  Purchase #3 $145.49   10.505%   $160.7737   $160.77   $160.75   $160.80  
  Purchase #4 $88.98   8.441%   $96.4908   $96.49   $96.50   $96.50  
  Purchase #5 $54.90   13.639%   $62.3878   $62.39   $62.40   $62.40  
  Purchase #6 $89.43   7.841%   $96.4422   $96.44   $96.45   $96.40  
  Purchase #7 $198.40   5.661%   $209.6314   $209.63   $209.65   $209.60  
  7 purchase totals = $696.09       $755.3389   $755.33   $755.40   $755.30