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 $69.96   5.244%   $73.6287   $73.63   $73.65   $73.60  
  Purchase #2 $9.58   13.341%   $10.8581   $10.86   $10.85   $10.90  
  Purchase #3 $129.69   8.715%   $140.9925   $140.99   $141.00   $141.00  
  Purchase #4 $92.45   5.304%   $97.3535   $97.35   $97.35   $97.40  
  Purchase #5 $78.85   5.634%   $83.2924   $83.29   $83.30   $83.30  
  Purchase #6 $85.91   3.611%   $89.0122   $89.01   $89.00   $89.00  
  Purchase #7 $143.31   7.423%   $153.9479   $153.95   $153.95   $153.90  
  7 purchase totals = $609.75       $649.0853   $649.08   $649.10   $649.10