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 $216.28   8.139%   $233.883   $233.88   $233.90   $233.90  
  Purchase #2 $135.40   9.629%   $148.4377   $148.44   $148.45   $148.40  
  Purchase #3 $44.28   12.228%   $49.6946   $49.69   $49.70   $49.70  
  Purchase #4 $20.79   9.236%   $22.7102   $22.71   $22.70   $22.70  
  Purchase #5 $200.49   12.241%   $225.032   $225.03   $225.05   $225.00  
  Purchase #6 $192.76   9.734%   $211.5233   $211.52   $211.50   $211.50  
  Purchase #7 $39.35   8.783%   $42.8061   $42.81   $42.80   $42.80  
  7 purchase totals = $849.35       $934.0869   $934.08   $934.10   $934.00