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 $88.46   11.155%   $98.3277   $98.33   $98.35   $98.30  
  Purchase #2 $151.59   7.494%   $162.9502   $162.95   $162.95   $163.00  
  Purchase #3 $130.52   3.283%   $134.805   $134.81   $134.80   $134.80  
  Purchase #4 $12.77   13.205%   $14.4563   $14.46   $14.45   $14.50  
  Purchase #5 $185.76   9.829%   $204.0184   $204.02   $204.00   $204.00  
  Purchase #6 $211.98   11.130%   $235.5734   $235.57   $235.55   $235.60  
  Purchase #7 $233.81   6.326%   $248.6008   $248.60   $248.60   $248.60  
  7 purchase totals = $1,014.89       $1,098.7318   $1,098.74   $1,098.70   $1,098.80