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 $64.39   4.298%   $67.1575   $67.16   $67.15   $67.20  
  Purchase #2 $168.31   10.662%   $186.2552   $186.26   $186.25   $186.30  
  Purchase #3 $97.62   9.576%   $106.9681   $106.97   $106.95   $107.00  
  Purchase #4 $170.59   3.414%   $176.4139   $176.41   $176.40   $176.40  
  Purchase #5 $153.46   9.469%   $167.9911   $167.99   $168.00   $168.00  
  Purchase #6 $191.55   10.750%   $212.1416   $212.14   $212.15   $212.10  
  Purchase #7 $39.97   13.409%   $45.3296   $45.33   $45.35   $45.30  
  7 purchase totals = $885.89       $962.2570   $962.26   $962.25   $962.30