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 $246.51   8.347%   $267.0862   $267.09   $267.10   $267.10  
  Purchase #2 $226.29   6.622%   $241.2749   $241.27   $241.25   $241.30  
  Purchase #3 $20.96   12.137%   $23.5039   $23.50   $23.50   $23.50  
  Purchase #4 $164.64   12.139%   $184.6256   $184.63   $184.65   $184.60  
  Purchase #5 $32.62   11.169%   $36.2633   $36.26   $36.25   $36.30  
  Purchase #6 $157.54   9.517%   $172.5331   $172.53   $172.55   $172.50  
  Purchase #7 $77.65   6.641%   $82.8067   $82.81   $82.80   $82.80  
  7 purchase totals = $926.21       $1,008.0937   $1,008.09   $1,008.10   $1,008.10