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 $62.71   13.627%   $71.2555   $71.26   $71.25   $71.30  
  Purchase #2 $146.56   5.861%   $155.1499   $155.15   $155.15   $155.10  
  Purchase #3 $186.32   10.325%   $205.5575   $205.56   $205.55   $205.60  
  Purchase #4 $136.99   13.214%   $155.0919   $155.09   $155.10   $155.10  
  Purchase #5 $234.92   5.817%   $248.5853   $248.59   $248.60   $248.60  
  Purchase #6 $26.62   11.736%   $29.7441   $29.74   $29.75   $29.70  
  Purchase #7 $82.33   7.142%   $88.21   $88.21   $88.20   $88.20  
  7 purchase totals = $876.45       $953.5942   $953.60   $953.60   $953.60