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 $56.81   13.178%   $64.2964   $64.30   $64.30   $64.30  
  Purchase #2 $108.60   6.433%   $115.5862   $115.59   $115.60   $115.60  
  Purchase #3 $93.51   3.560%   $96.839   $96.84   $96.85   $96.80  
  Purchase #4 $162.55   7.281%   $174.3853   $174.39   $174.40   $174.40  
  Purchase #5 $53.57   11.128%   $59.5313   $59.53   $59.55   $59.50  
  Purchase #6 $112.44   12.134%   $126.0835   $126.08   $126.10   $126.10  
  Purchase #7 $203.43   10.110%   $223.9968   $224.00   $224.00   $224.00  
  7 purchase totals = $790.91       $860.7185   $860.73   $860.80   $860.70