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 $205.51   10.703%   $227.5057   $227.51   $227.50   $227.50  
  Purchase #2 $106.30   7.110%   $113.8579   $113.86   $113.85   $113.90  
  Purchase #3 $85.42   8.641%   $92.8011   $92.80   $92.80   $92.80  
  Purchase #4 $160.30   11.689%   $179.0375   $179.04   $179.05   $179.00  
  Purchase #5 $147.34   13.667%   $167.477   $167.48   $167.50   $167.50  
  Purchase #6 $209.88   7.871%   $226.3997   $226.40   $226.40   $226.40  
  Purchase #7 $160.28   12.425%   $180.1948   $180.19   $180.20   $180.20  
  7 purchase totals = $1,075.03       $1,187.2737   $1,187.28   $1,187.30   $1,187.30