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 $52.51   6.795%   $56.0781   $56.08   $56.10   $56.10  
  Purchase #2 $113.95   10.797%   $126.2532   $126.25   $126.25   $126.30  
  Purchase #3 $206.32   13.466%   $234.1031   $234.10   $234.10   $234.10  
  Purchase #4 $212.50   4.177%   $221.3761   $221.38   $221.40   $221.40  
  Purchase #5 $155.66   12.874%   $175.6997   $175.70   $175.70   $175.70  
  Purchase #6 $207.57   4.157%   $216.1987   $216.20   $216.20   $216.20  
  Purchase #7 $55.49   11.753%   $62.0117   $62.01   $62.00   $62.00  
  7 purchase totals = $1,004.00       $1,091.7206   $1,091.72   $1,091.75   $1,091.80