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 $147.47   13.872%   $167.927   $167.93   $167.95   $167.90  
  Purchase #2 $115.55   7.659%   $124.4   $124.40   $124.40   $124.40  
  Purchase #3 $71.29   8.409%   $77.2848   $77.28   $77.30   $77.30  
  Purchase #4 $154.60   5.485%   $163.0798   $163.08   $163.10   $163.10  
  Purchase #5 $133.74   10.348%   $147.5794   $147.58   $147.60   $147.60  
  Purchase #6 $85.93   9.595%   $94.175   $94.18   $94.20   $94.20  
  Purchase #7 $64.33   9.718%   $70.5816   $70.58   $70.60   $70.60  
  7 purchase totals = $772.91       $845.0276   $845.03   $845.15   $845.10