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 $247.43   11.652%   $276.2605   $276.26   $276.25   $276.30  
  Purchase #2 $250.65   10.216%   $276.2564   $276.26   $276.25   $276.30  
  Purchase #3 $143.96   9.419%   $157.5196   $157.52   $157.50   $157.50  
  Purchase #4 $16.52   6.698%   $17.6265   $17.63   $17.65   $17.60  
  Purchase #5 $75.82   11.382%   $84.4498   $84.45   $84.45   $84.40  
  Purchase #6 $134.75   7.253%   $144.5234   $144.52   $144.50   $144.50  
  Purchase #7 $109.33   8.218%   $118.3147   $118.31   $118.30   $118.30  
  7 purchase totals = $978.46       $1,074.9509   $1,074.95   $1,074.90   $1,074.90