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 $9.96   13.217%   $11.2764   $11.28   $11.30   $11.30  
  Purchase #2 $243.58   10.688%   $269.6138   $269.61   $269.60   $269.60  
  Purchase #3 $36.66   5.797%   $38.7852   $38.79   $38.80   $38.80  
  Purchase #4 $224.72   8.224%   $243.201   $243.20   $243.20   $243.20  
  Purchase #5 $71.69   13.763%   $81.5567   $81.56   $81.55   $81.60  
  Purchase #6 $25.84   7.702%   $27.8302   $27.83   $27.85   $27.80  
  Purchase #7 $238.58   5.620%   $251.9882   $251.99   $252.00   $252.00  
  7 purchase totals = $851.03       $924.2515   $924.26   $924.30   $924.30