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 $219.60   13.280%   $248.7629   $248.76   $248.75   $248.80  
  Purchase #2 $86.25   8.146%   $93.2759   $93.28   $93.30   $93.30  
  Purchase #3 $105.46   5.471%   $111.2297   $111.23   $111.25   $111.20  
  Purchase #4 $190.67   11.595%   $212.7782   $212.78   $212.80   $212.80  
  Purchase #5 $54.28   5.550%   $57.2925   $57.29   $57.30   $57.30  
  Purchase #6 $153.57   11.407%   $171.0877   $171.09   $171.10   $171.10  
  Purchase #7 $160.63   11.311%   $178.7989   $178.80   $178.80   $178.80  
  7 purchase totals = $970.46       $1,073.2258   $1,073.23   $1,073.30   $1,073.30