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 $109.25   13.772%   $124.2959   $124.30   $124.30   $124.30  
  Purchase #2 $61.51   13.701%   $69.9375   $69.94   $69.95   $69.90  
  Purchase #3 $124.55   12.220%   $139.77   $139.77   $139.75   $139.80  
  Purchase #4 $42.35   8.129%   $45.7926   $45.79   $45.80   $45.80  
  Purchase #5 $52.73   6.737%   $56.2824   $56.28   $56.30   $56.30  
  Purchase #6 $238.74   6.394%   $254.005   $254.01   $254.00   $254.00  
  Purchase #7 $174.78   12.722%   $197.0155   $197.02   $197.00   $197.00  
  7 purchase totals = $803.91       $887.0989   $887.11   $887.10   $887.10