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 $246.27   6.499%   $262.2751   $262.28   $262.30   $262.30  
  Purchase #2 $62.95   5.861%   $66.6395   $66.64   $66.65   $66.60  
  Purchase #3 $149.59   3.489%   $154.8092   $154.81   $154.80   $154.80  
  Purchase #4 $243.78   13.253%   $276.0882   $276.09   $276.10   $276.10  
  Purchase #5 $106.56   10.710%   $117.9726   $117.97   $117.95   $118.00  
  Purchase #6 $20.61   13.508%   $23.394   $23.39   $23.40   $23.40  
  Purchase #7 $166.62   10.343%   $183.8535   $183.85   $183.85   $183.90  
  7 purchase totals = $996.38       $1,085.0321   $1,085.03   $1,085.05   $1,085.10