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 $241.92   8.637%   $262.8146   $262.81   $262.80   $262.80  
  Purchase #2 $141.35   5.170%   $148.6578   $148.66   $148.65   $148.70  
  Purchase #3 $59.85   3.123%   $61.7191   $61.72   $61.70   $61.70  
  Purchase #4 $158.37   5.294%   $166.7541   $166.75   $166.75   $166.80  
  Purchase #5 $133.37   6.127%   $141.5416   $141.54   $141.55   $141.50  
  Purchase #6 $55.60   3.291%   $57.4298   $57.43   $57.45   $57.40  
  Purchase #7 $124.45   8.721%   $135.3033   $135.30   $135.30   $135.30  
  7 purchase totals = $914.91       $974.2203   $974.21   $974.20   $974.20