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 $65.58   8.768%   $71.3301   $71.33   $71.35   $71.30  
  Purchase #2 $227.81   12.536%   $256.3683   $256.37   $256.35   $256.40  
  Purchase #3 $224.88   10.527%   $248.5531   $248.55   $248.55   $248.60  
  Purchase #4 $245.57   7.195%   $263.2388   $263.24   $263.25   $263.20  
  Purchase #5 $159.76   5.825%   $169.066   $169.07   $169.05   $169.10  
  Purchase #6 $197.43   10.200%   $217.5679   $217.57   $217.55   $217.60  
  Purchase #7 $39.95   4.155%   $41.6099   $41.61   $41.60   $41.60  
  7 purchase totals = $1,160.98       $1,267.7341   $1,267.74   $1,267.70   $1,267.80