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 $154.87   10.686%   $171.4194   $171.42   $171.40   $171.40  
  Purchase #2 $99.57   7.441%   $106.979   $106.98   $107.00   $107.00  
  Purchase #3 $164.26   8.780%   $178.682   $178.68   $178.70   $178.70  
  Purchase #4 $100.80   13.343%   $114.2497   $114.25   $114.25   $114.20  
  Purchase #5 $219.56   4.444%   $229.3172   $229.32   $229.30   $229.30  
  Purchase #6 $191.38   8.627%   $207.8904   $207.89   $207.90   $207.90  
  Purchase #7 $69.83   7.767%   $75.2537   $75.25   $75.25   $75.30  
  7 purchase totals = $1,000.27       $1,083.7914   $1,083.79   $1,083.80   $1,083.80