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 $209.36   8.211%   $226.5505   $226.55   $226.55   $226.60  
  Purchase #2 $122.52   4.173%   $127.6328   $127.63   $127.65   $127.60  
  Purchase #3 $164.99   9.211%   $180.1872   $180.19   $180.20   $180.20  
  Purchase #4 $93.60   9.195%   $102.2065   $102.21   $102.20   $102.20  
  Purchase #5 $50.62   12.499%   $56.947   $56.95   $56.95   $56.90  
  Purchase #6 $189.33   4.410%   $197.6795   $197.68   $197.70   $197.70  
  Purchase #7 $143.25   8.279%   $155.1097   $155.11   $155.10   $155.10  
  7 purchase totals = $973.67       $1,046.3132   $1,046.32   $1,046.35   $1,046.30