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 $159.96   10.501%   $176.7574   $176.76   $176.75   $176.80  
  Purchase #2 $60.41   3.231%   $62.3618   $62.36   $62.35   $62.40  
  Purchase #3 $166.62   5.340%   $175.5175   $175.52   $175.50   $175.50  
  Purchase #4 $57.64   9.402%   $63.0593   $63.06   $63.05   $63.10  
  Purchase #5 $178.49   3.603%   $184.921   $184.92   $184.90   $184.90  
  Purchase #6 $110.91   8.545%   $120.3873   $120.39   $120.40   $120.40  
  Purchase #7 $229.51   4.661%   $240.2075   $240.21   $240.20   $240.20  
  7 purchase totals = $963.54       $1,023.2118   $1,023.22   $1,023.15   $1,023.30