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 $43.41   13.258%   $49.1653   $49.17   $49.15   $49.20  
  Purchase #2 $105.52   8.319%   $114.2982   $114.30   $114.30   $114.30  
  Purchase #3 $246.85   7.272%   $264.8009   $264.80   $264.80   $264.80  
  Purchase #4 $193.33   7.256%   $207.358   $207.36   $207.35   $207.40  
  Purchase #5 $37.70   10.842%   $41.7874   $41.79   $41.80   $41.80  
  Purchase #6 $237.34   11.406%   $264.411   $264.41   $264.40   $264.40  
  Purchase #7 $201.35   10.246%   $221.9803   $221.98   $222.00   $222.00  
  7 purchase totals = $1,065.50       $1,163.8011   $1,163.81   $1,163.80   $1,163.90