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 $204.69   6.395%   $217.7799   $217.78   $217.80   $217.80  
  Purchase #2 $57.73   13.491%   $65.5184   $65.52   $65.50   $65.50  
  Purchase #3 $109.78   13.769%   $124.8956   $124.90   $124.90   $124.90  
  Purchase #4 $243.90   11.348%   $271.5778   $271.58   $271.60   $271.60  
  Purchase #5 $123.85   5.127%   $130.1998   $130.20   $130.20   $130.20  
  Purchase #6 $27.51   5.861%   $29.1224   $29.12   $29.10   $29.10  
  Purchase #7 $180.69   3.810%   $187.5743   $187.57   $187.55   $187.60  
  7 purchase totals = $948.15       $1,026.6682   $1,026.67   $1,026.65   $1,026.70