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 $216.98   11.323%   $241.5486   $241.55   $241.55   $241.50  
  Purchase #2 $105.84   7.386%   $113.6573   $113.66   $113.65   $113.70  
  Purchase #3 $7.45   12.563%   $8.3859   $8.39   $8.40   $8.40  
  Purchase #4 $157.33   10.839%   $174.383   $174.38   $174.40   $174.40  
  Purchase #5 $238.61   3.836%   $247.7631   $247.76   $247.75   $247.80  
  Purchase #6 $8.30   9.343%   $9.0755   $9.08   $9.10   $9.10  
  Purchase #7 $192.45   11.167%   $213.9409   $213.94   $213.95   $213.90  
  7 purchase totals = $926.96       $1,008.7543   $1,008.76   $1,008.80   $1,008.80