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 $235.83   4.157%   $245.6335   $245.63   $245.65   $245.60  
  Purchase #2 $52.33   10.827%   $57.9958   $58.00   $58.00   $58.00  
  Purchase #3 $169.28   5.331%   $178.3043   $178.30   $178.30   $178.30  
  Purchase #4 $66.52   10.759%   $73.6769   $73.68   $73.70   $73.70  
  Purchase #5 $103.41   10.526%   $114.2949   $114.29   $114.30   $114.30  
  Purchase #6 $163.65   7.232%   $175.4852   $175.49   $175.50   $175.50  
  Purchase #7 $60.80   12.176%   $68.203   $68.20   $68.20   $68.20  
  7 purchase totals = $851.82       $913.5936   $913.59   $913.65   $913.60