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 $60.76   6.815%   $64.9008   $64.90   $64.90   $64.90  
  Purchase #2 $197.55   4.376%   $206.1948   $206.19   $206.20   $206.20  
  Purchase #3 $50.68   4.801%   $53.1131   $53.11   $53.10   $53.10  
  Purchase #4 $155.89   9.263%   $170.3301   $170.33   $170.35   $170.30  
  Purchase #5 $106.38   5.694%   $112.4373   $112.44   $112.45   $112.40  
  Purchase #6 $219.59   8.351%   $237.928   $237.93   $237.95   $237.90  
  Purchase #7 $38.58   10.519%   $42.6382   $42.64   $42.65   $42.60  
  7 purchase totals = $829.43       $887.5423   $887.54   $887.60   $887.40