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 $45.48   9.283%   $49.7019   $49.70   $49.70   $49.70  
  Purchase #2 $190.73   8.278%   $206.5186   $206.52   $206.50   $206.50  
  Purchase #3 $107.45   10.735%   $118.9848   $118.98   $119.00   $119.00  
  Purchase #4 $72.40   5.421%   $76.3248   $76.32   $76.30   $76.30  
  Purchase #5 $163.53   7.845%   $176.3589   $176.36   $176.35   $176.40  
  Purchase #6 $150.93   12.118%   $169.2197   $169.22   $169.20   $169.20  
  Purchase #7 $112.42   8.709%   $122.2107   $122.21   $122.20   $122.20  
  7 purchase totals = $842.94       $919.3194   $919.31   $919.25   $919.30