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 $232.80   11.329%   $259.1739   $259.17   $259.15   $259.20  
  Purchase #2 $59.77   7.795%   $64.4291   $64.43   $64.45   $64.40  
  Purchase #3 $78.41   10.564%   $86.6932   $86.69   $86.70   $86.70  
  Purchase #4 $237.96   4.771%   $249.3131   $249.31   $249.30   $249.30  
  Purchase #5 $233.73   12.797%   $263.6404   $263.64   $263.65   $263.60  
  Purchase #6 $22.95   3.335%   $23.7154   $23.72   $23.70   $23.70  
  Purchase #7 $44.31   11.415%   $49.368   $49.37   $49.35   $49.40  
  7 purchase totals = $909.93       $996.3331   $996.33   $996.30   $996.30